MixinBootstrap Mod 1.17.1/1.16.5/1.15.2 gives a temporary way to boot Mixin in a MinecraftForge production environment. Note that it is not the official method of loading Mixin!

About MixinBootstrap
Mixin is available in Forge 1.15.2-31.2.44+ and 1.16.1-32.0.72+.
It’s not too difficult for you to use. What you need to do is to drop the MixinBootstrap-.jar into the MinecraftForge mods folder.
The Apache 2.0 license allows the present release.
The MIT license enables Mixin.
It’s free for you to include the current edition in your mod pack.
In case it’s crashing your game, please move to your mods folder and right-click on its mod’s jar file. Then, press delete.
Fruit Trees, Snow! Real Magic!, All the Mod 5, etc. are supported mods.
MixinBootstrap is an API and Library mod. It provides the user a manner to start Mixin temporarily. Before you begin to check anything, you have to download and install Minecraft Forge first!