I found a Minecraft server that is on version 1.21.5 and it is just a simple join up kind of server
The post does not say any special modes or rules so it feels like you just hop in and start playing
JOIN THIS 1.21.5 SERVER NOW
GG.MINEWIND.NET New Server IPRatchy SMP Lifesteal Vanilla Chaos
I found Ratchy SMP and it is a survival server that is mostly vanilla but it uses modpacks too.
The main one mentioned is Lifesteal so players can take hearts and you can also turn hearts into items with a simple command.
The commands are meant to be easy and the owner said they made it for fun. They also said the server can be down sometimes for mod maintenance and you can comment if you want to add mods.
GG.MINEWIND.NET New Server IP