I found Xapros SMP and it is a chill vanilla server for adults on Minecraft 1.21.11.
The server is meant for long term play since it started in January 2025 and they say they will not reset. It is good for big projects and megabuilds and there is no world border so you can go really far out.
People play from lots of places around the world so someone is usually online. They say peak time is about 20 to 25 players.
It stays close to singleplayer because it runs on Fabric not Spigot or Paper so redstone and farms should act normal. They also have BlazeandCave advancements for extra goals.
There are no land claims but griefing and theft are not allowed. There is a ledger inspect command so you can check what happened if stuff goes missing.
Spawn is built up and there is a diamond based shopping area. Travel is fast with Nether ice boat highways and there is Bluemap so you can view the world map.
