See this about MC 1.20.5 and later versions

https://old.reddit.com/r/litematica/comments/1di4o3h/announcement_about_litematicas_future_and_updates/

TL;DR; I won't maintain the 1.20.5+ versions myself anymore, at least for now. There are ports by Sakura-Ryoko. They will be here once they are more stable, see the post for the links and details before then.

Description

A client-side mod that allows displaying various "info lines" on the screen ("mini-F3"). The alignment (screen corner), background and text color and font size are configurable. Note: This is a client-side-only mod! You can't put it on a server.

The mod also has various "overlay renderers", such as:

Structure Bounding Boxes (These only work in single player, without a server-side mod! Currently the only server-side mods that send the data in a format that MiniHUD knows about are Servux and QuickCarpet. If you have FabricCarpet, then you also need Servux.
Spawn Chunks
Light Level overlay with markers and/or numbers (configurable)
Region File Boundaries
Random Tick range
Shapes: A mob Despawn Sphere, plus 24 and 32 block Spawn Spheres, a generic configurable radius Sphere, a Circle/Cylinder. More shapes are also planned.
Block Grid
Mob spawn algorithm chunks range (< 1.14 only, in 1.14+ it's the same as the random ticked chunks)
Height map (used by the mob spawn algorithm)

(note that many of these currently are only available in the more recent LiteLoader, Rift and Fabric versions.)
The mod also adds hotkeys for toggling on/off the vanilla debug renderers for blocks collision boxes, heightmap, entity path finding etc.
The displayed information lines can also be toggled on/off with hotkeys, and the HUD itself can be toggled ON and OFF.
Some example screenshots are on the Images page.

Generic info

The default in-game config menu hotkey is H + C
The default on/off toggle key is H
You can provide the world seed for MiniHUD (only used for the Slime Chunks info line and overlay) in multiplayer either by running the vanilla /seed command if you have the permission, or you can give it manually with a regular chat message in the form minihud-seed 12345. In single player the mod grabs the seed directly.

NOTE: MiniHUD also requires the MaLiLib library mod.
Be sure to download the correct version of both mods from the Files page!
https://www.curseforge.com/minecraft/mc-mods/malilib

Overlay colors are all opaque, what to do?!

In the current 0.19.0-dev versions for MC 1.16+, there are a bunch of features that are temporarily ported over from the main development version on 1.12.2. Due to it being a temporary port, I didn't bother trying to fix everything that is broken due to there being missing things in malilib, and there is currently also a bug in malilib's Color Edit menu in 1.13.2+ which causes the alpha channel (transparency) to reset to fully opaque when you use the Color Editor menu.

So currently, until the new malilib and other mod updates with the latest code from 1.12.2 can happen, you just have to manually fix the color value after using the color editor. Basically you just need to change the first two letters (after the #) in the hex color code from FF (fully opaque) to something between 30 to 60 or so, and then toggle off/on the overlay or shape in question to update it.

Different mod loaders vs. mod versions

There are different versions of MiniHUD available for different mod loaders on different Minecraft versions.
Be sure to download the correct version for the mod loader you are using!
The newer builds will all include the mod loader name in the mod filename.

For MC 1.13.2 there are versions for the Rift mod loader. Those versions have '-rift' in their filename.
(Also note that the 1.13.2 versions ONLY work on MC 1.13.2, and NOT on the earlier 1.13 versions!)
For MC 1.14.x there are currently versions for the Fabric mod loader, those versions have '-fabric' in their filename.
Future Forge versions will also include -forge in the mod file name.

Key combinations

The mod's main rendering toggle key is by default H.
The in-game config menu hotkey is by default H + C.

Recent MiniHUD versions that use malilib

For the more recent versions of MiniHUD that use malilib, all the hotkeys are in MiniHUD's own in-game config menu, which by default opens with H + C.

Old Forge versions of MiniHUD

For the old Forge versions of the mod, the keybinds can be changed in the vanilla Controls menu.

For the old Forge versions:

Toggle Mode key (by itself): Toggle the HUD state ON/OFF.
Toggle Mode key + "info key": Toggle ON/OFF the different pieces of information (the keys can be set in the mod configs).

Available information

NOTE: The information below this is outdated and doesn't include everything that is in the recent LiteLoader, Rift and Fabric versions of the mod.
Look through the in-game config menu to see everything that is available in addition to the things mentioned below.

The following information is currently available:

Real time (ie. a clock...)
World time in ticks
World time formatted to days, hours, minutes
Player's current block position
Player's current position in chunk
Player's coordinates
Player's current dimension ID
Player's yaw rotation
Player's pitch rotation
Player's current moving speed
Player's facing
The Chunk the player is currently in
The region file the player is currently in
Looked-at-entity's name and health
Looked-at-entity's registry name (1.11+) or ID (1.10.2)
The block the player is looking at
Block's registry name and the BlockState properties of the looked-at-block (like on the F3 screen)
Current light level
Current biome
Current biome's registry name.
Current FPS
Entity count
C value (rendered chunk sections) from F3
P value (number of particles) from F3
Current local difficulty number (from F3)
Is the current chunk a slime chunk. Note: in multiplayer you need to manually run the /seed command!

Starting from version 0.13.0, there is now a region file boundary overlay renderer. The default hotkey to toggle it ON/OFF is Toggle (H) + J.

Note: Starting from version 0.9.0, you can change all these quick toggle keys via the config file or the in-game config menu.
Note: Starting from version 0.11.0, you can change the order of these info lines via the config file or the in-game config menu.

To temporarily (= not saved in the configs) toggle the info types while in-game, do this:

In version 0.9.0 or later, press and hold the main Toggle key, and then press the configured hotkey for the info type you want to toggle
Before version 0.9.0, first press and hold the indicated info type key and then press the Toggle key

Old Configuration options

Below are the bit mask values for the different information types. This is now redundant, just use the on/off options in the in-game config menu instead!
These were removed entirely in version 0.11.0.

The bit mask values of the enabled-by-default information is as follows:

1 = coordinates
2 = yaw
4 = pitch
8 = speed
16 = biome
32 = light level
64 = facing
128 = block position
256 = chunk position
512 = block looking at
1024 = fps
2048 = entity count
4096 = dimension id
8192 = world time (ticks)
16384 = world time (formatted)
32768 = IRL time (ie. a clock)
65536 = looking at entity
131072 = slime chunk
262144 = blockstate properties

Sum together the ones you want enabled by default. This means that those will show up when you load the game and then enable the MiniHUD by pressing the Toggle key.

Configuration

There are a few things that can be adjusted either via the in-game configuration menu or in the configuration file.

The information to be displayed on the Info Lines HUD
Font scale factor
The font and backgrond colors
Whether to use a font shadow in the text rendering
Whether to use a background color for the text
Whether to sort the displayed information lines by their length
Whether to reverse the above mentioned sorting order
Whether to use a custom format string for the coordinate line, and the format string to use
Multiple options to configure the Light Level overlay
The colors of all the overlay renderers

Note: The custom format string for the coordinates has to have three float number format specifiers.
An example of that would be "X: %.1f Y: %.1f Z: %.1f" (without the quotes) to give an output like: X: 1234.2 Y: 64.0 Z: 4321.7.

Vanilla debug renderers

Starting from mod version 0.12.0, there are hotkeys to toggle ON/OFF the debug renderers that exist in vanilla, but are normally not usable/accessible. The hotkeys for these can be set in the Hotkeys config category. Note: The neighbor updates debug renderer only works in single player.
Note: The pathfinding debug renderer also only works in single player, unless another mod sends the appropriate custom payload vanilla packet from the server, to add the path data to the debug renderer. Currently I'm not aware of any such mods however.

Some example screenshots of the debug renderers: Collision boxes:

Height map:

Neighbor updates:

Pathfinding:

Solid block faces:

Water:

Snapshot versions and latest development builds

There are (at least at times) versions of my mods available for the latest Minecraft snapshots here: https://masa.dy.fi/mcmods/client_mods/
That page also sometimes includes newer development builds than what is available here on CurseForge.
If you encounter bugs, then try to update all the mods (from the ones that you use) from that page to see if the issue has been fixed already.
(There are at times changes in malilib or the mods that require both of them to be updated at the same time!)

If you have questions or need help with something, the best/fastest way to get answers is on my Discord server.