I found Xapros SMP and it is a chill vanilla server made for adults. It is on Minecraft 1.21.11 and the world started in January 2025. They say it will not reset so it is good for long term bases and huge builds.
The community is 18+ and spread around the world so you can usually find someone online. Peak time is around 20 to 25 players and it does not feel empty.
It runs on Fabric instead of Paper so redstone and farms act like singleplayer. The server also aims for strong performance and low lag.
There are no land claims but griefing and stealing are not allowed. There is an inspect command with ledger so you can check what happened if something goes missing.
There is a nice spawn plus player shops with a diamond economy. Travel is easy with nether ice boat highways and there is a bluemap you can use to look at the world. There is no world border so you can live as far out as you want. Phantoms can be toggled per player and BlazeandCave advancements are included for extra goals.
