It's impossible to create a 1.12.2 tfc server because it glitches insanely right after creating the world and the created world is always vanilla.

level type tfc_classic or delete server.properties and world and try again.

I noticed that, the server always creates a vanilla world, if level_type=default.

Should TFC-TNG automatically re-write this setting? (just like single user world)

https://terrafirmacraft.com/f/topic/10286-my-server-only-generates-a-vanilla-world/

If the server.properties does not already exist, we do default it. We do not rewrite it if the world already exists as that is a recipe for causing problems.

It seems that there's no documentation, and no warning for that. That's sometimes confusing...

Maybe it's better to add a documentation entry on TFC wiki, or print a warning message in server log.