serverside mods ONLY ?

I'm about to start a vanilla server with several friends, and we've agreed to only use serverside mods and a few plugins. While searching, I only found one post here from 8 years ago about this.

Could you recommend some good and fun serverside ONLY mods for 1.21+? Regarding terrain generation mods, I haven't decided which one to use yet. Which ones do you like best?

(Suggestions for plugins that work with Fabric would also be great; I'm willing to buy paid plugins as well.)