Install an Essentials Mods [FORGE] - 1.21 RELEASE! server through the Control Panel (Servers → Select your server → Game servers → Add Game Server → Essentials Mods [FORGE] - 1.21 RELEASE!)
It works really well. Very easy to setup. You can modify any setting in the game. The fact that anyone can join the server and how easy it is to manage is really useful. The fact that it is very cheap but works so well for its price it is amazing. So glad I found this website.