I found a public SMP for Java 1.21.
It is a simple survival multiplayer server that is open for anyone to join and play.
Public Java 1.21 SMP Just Opened
java edition playersmake new friendsnew player friendlypublic multiplayer serversurvival building focus
GG.MINEWIND.NET New Server IPCozy Semi Vanilla Java SMP
cooperative survival focusFriendly Survival Worldreturning player spotsmall group energyVanilla-style gameplay
I found a simple cozy SMP that is semi vanilla and runs on Java.
It feels like a straightforward place where you just join in and play survival with other people. The whole point is keeping it cozy and easy to get into.
GG.MINEWIND.NET New Server IP