I don´t know if this issue is known, however, let me state that i´m using a mod that ports fabric mods for forge with the help of the mods connector, connector extras and fabric api
Modpack listed below:

The connector mods creates other .jar files to map the variables i presume, but that folder won´t help much to track the issue (if it is an issue)

Updating with the "adaptor" mods i downloaded:

https://www.curseforge.com/minecraft/mc-mods/sinytra-connector
https://www.curseforge.com/minecraft/mc-mods/connector-extras
https://www.curseforge.com/minecraft/mc-mods/forgified-fabric-api

This is a duplicate, please see: #27