Monsterley_128_bop_201206.zip is a release file of the Minecraft resource pack Monsterley HD Add-On: Biomes O' Plenty, made for Minecraft 1.16.3, 1.16.4. It was published on December 6, 2020 and is 12.2 MB in size. For the full description, screenshots and every other version, visit the Monsterley HD Add-On: Biomes O' Plenty resource pack page.
How to install: Put the .zip into .minecraft/resourcepacks (do not extract it) and enable it under Options → Resource Packs.