Consider https://www.curseforge.com/minecraft/mc-mods/mybrightness as a "drop-in" replacement for GammaBright, only using Fabric instead of LiteLoader. The LiteLoader project appears to be dead on 1.12, and for 1.14.4 the functionality of LiteLoader appears to be replaced by Fabric Mod. For details on getting up and running with Fabric, look for VoxelMap which made the switch from LiteLoader to Fabric for 1.14. A few other former "LiteLoader" mods have made this switch as well, but VoxelMap's guide is what I refer to. Once you have VoxelMap working, grab a copy from the MyBrightness link above.