One of your mods is trying to load client side only classes on the server.
That log does not say which mod, but the logs/debug.log might.
You should remove any (broken) client side only mods you have installed from the server.
Issue with the supplementaries mod. Something related to your key bindings configuration?
Check you have the latest version then contact the mod author.
Maybe related? You should upgrade optifine to the latest preview release or try without optifine.
It still doesn't say which config file.
But looking at the source code for the mod, the file is config/terrablender.toml
https://github.com/Glitchfiend/TerraBlender/blob/dde0781f3d2b81bfc262c6c99e0ac5f1794c37b6/Forge/src/main/java/terrablender/core/TerraBlenderForge.java#L30