I am using the PaperMC Server version paper-1.16.4-328.jar and have no plugins installed besides phosphor-fabric. I am using the latest phosphor-fabric release version phosphor-fabric-mc1.16.3-0.7.0+build.10.jar and experience an error in loading the plugin. The log can be found here: https://del.dog/cowulamuyt.txt

When compiling lithium-fabric with all the latest commits, the same error can be observed

Lithium and Phosphor are Fabric mods, not Paper plugins. You can learn more about the Fabric modding toolchain at https://fabricmc.net

I see, only found out now that fabric servers exist. Thank you.