MixinBootstrap is needed to run some popular mods, for example, Forge version of Immersive Portals. It is necessary to use the Mixin framework and does not affect the game. Installing it is only necessary if one of the mods requires it.
How to install MixinBootstrap mod
- Make sure you have installed Minecraft Forge.
- Download the mod for your version of the game.
- Put it in the ‘mods’ folder, which is located in the game folder.