I found WBPVP which is a Java server running on 1.21.11 and it is focused on 1.9 style PvP.
It has normal gamemodes and the main new thing is Water Bucket PVP. You fight on a floating island and try to knock the other player off like sumo.
The twist is you can water bucket clutch and come back up so the fights can get wild and clutchy. It feels like a simple idea but it turns into lots of quick saves and comebacks.
