• Mod 'SimpleHats' (simplehats) 1.18.2-0.1.0 requires version 0.55.1 or later of mod 'Fabric API' (fabric), but only the wrong version is present: 0.51.1+1.18.2!
  But the renderer used by my fabric client is optifabric+optifine because their light and shadow frame performance is much better than other renderers. I don’t know if you will downgrade the requirement of mod to use fabric api to 0.51.1
  Now optifabric+optifine only supports the 0.51.1 fabric api and does not support the latest version of the api
  The bug is the inability to enter/create the world
  latest.log

Ill see if I can lower the required version, no idea if it'll cause other random issues.

Unfortunately it seems the version of Fabric API that breaks compatibility with OptiFabric is a single version lower than a version with API methods I require for SimpleHats, so I can't lower the required version to work with OptiFabric.
OptiFabric will need to update and fix its incompatability with newer Fabric API versions.

However, if you are using OptiFabric+Optifine for performance, you should switch to using other mods https://gist.github.com/modmuss50/deff1658c4550ca8b16cb5d40ceaa468#Sodium as even stated on OptiFabric's page itself.

OptiFabric has released new versions that fix their incompatibility, it loads fine now with SimpleHats and updated Fabric API, closing as resolved.