This is the datapack version of the original Nether Islands mod. With better noise settings modification support in vanilla Minecraft, it's much easier for you and me to edit the generation!
To edit the datapack, please refer to the GitHub repository's README.
Below is the old description copy-pasted from the mod page, just for reference:
A mod request from a friend to override the Nether's generation and remove the bedrock roof. Designed specifically for Comfy Winter and Better MC Skyblock, but you may include it in any modpack as you want.
I mean, this looks cool as heck (image taken with Oh the Biomes You'll Go)

You can configure this mod by editing "config/netherislands.json". It currently only has 2 things to configure though.
minY: The minimum Y-level of the dimension. Default: 0
height: The world height for the dimension. Default: 256
seaLevel: The sea level (a.k.a. lava level) of the dimension. Setting this to equal or below minY will remove all lava. Default: 0
bedrockFloorPosition: The Y-level of the bedrock floor. Setting this to below minY will remove the layer. Default: -10
The config file should look like this:

If you have discovered more issues, you may report them on GitHub or join my Discord server.
The 1.19 version of this mod isn't too customizable. Floating Islands generation for the Nether is hard-coded and cannot be changed with config.