I found Goober SMP and it is a brand new Vanilla plus Java server. It started just a few days ago and it already has around 20 active players so it feels alive.
The server is mostly vanilla but it adds small stuff to make multiplayer more fun. PvP is allowed and people are into building and hanging out so you can fight or make cool projects.
It runs on Java 1.21.11 and it has whitelist on so you need to get added before you can play. It also supports SVC mods and has a head drop plugin so players can drop their heads.
They want a player driven world with towns and community builds. Server wide events are planned too so sometimes it can get chaotic.