CrankHouse is a Semi-Anarchy Survival SMP with a pretty simple goal: keep the world as close to vanilla as possible, especially when it comes to mob rates, caps, and behavior, while still keeping the server stable for everyone, whether you play clean or use clients and mods.
The server runs on versions 1.17 through 1.20, and the focus is clearly on stability and a solid play environment. They've put a lot into the hardware side so the server can stay smooth and consistent instead of feeling rough or overloaded.
Modded or hacked clients are allowed here, but there are limits. Stuff like offhand bans, chunk bans, and similar abuse tools isn't tolerated, and the server will kick you automatically until the module is turned off. So yeah, you can play with clients, just don't be shady with them.