Simple: I installed the latest fabric (0.12.5), fabric api, optifine, and optifabric. But when I try to start mc, the game crashes, saying that optifabric only supports 0.8 - 0.12, and so 0.12.5 is not supported. The curseforge page said that optifabric supported every new fabric release?

Full message:
net.fabricmc.loader.impl.discovery.ModResolutionException: Mod resolution encountered an incompatible mod set!
A potential solution has been determined:
- Remove mod 'OptiFabric' (optifabric) 1.11.9 (C:\Users\Ezekiel\AppData\Roaming.minecraft\mods\optifabric-1.11.9.jar).
Unmet dependency listing:
- Mod 'OptiFabric' (optifabric) requires any version between 0.8.0 (inclusive) and 0.12 (exclusive) of mod 'Fabric Loader' (fabricloader), but only the wrong version is present: 0.12.5!
- Mod 'Fabric Loader' (fabricloader) 0.12.5 is being loaded from C:\Users\Ezekiel\AppData\Roaming.minecraft\libraries\net\fabricmc\fabric-loader\0.12.5\fabric-loader-0.12.5.jar
Inactive mods:
- mod 'OptiFabric' (optifabric) 1.11.9, reason: to remove
- mod 'Manningham Mills' (mm) 2.2, reason: inactive parent mod (nested jar)
at net.fabricmc.loader.impl.discovery.ModResolver.findCompatibleSet(ModResolver.java:183)
at net.fabricmc.loader.impl.discovery.ModResolver.resolve(ModResolver.java:48)
at net.fabricmc.loader.impl.FabricLoaderImpl.setup(FabricLoaderImpl.java:203)
at net.fabricmc.loader.impl.FabricLoaderImpl.load(FabricLoaderImpl.java:183)
at net.fabricmc.loader.impl.launch.knot.Knot.init(Knot.java:119)
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:68)
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)

Update your optifabric to 1.12.5

It says that version of 1.12.5 is 1.17.1 though? I'm trying to use MC version 1.16.5 ??

1.12.5 for version 1.16.5 is in CF

Duplicate of #394

The OptiFabric versions are backwards compatible (at the moment at least), so if you really wanted you could use OptiFabric v1.12.5 all the way back to 1.16.1