I couldn't get this to work by itself either. There was no SHIFT+L functionality, although the top bar showing that I was in an unclaimed area did show, so I know the mod loaded, at least partially.
When I installed the World Protection plugin I got the SHIFT+L functionality (WorldProtection, Self claim protection plugin).
I extracted both into their own folders in the Plugins directory. Extracting this one in just the Plugins directly without it being in its own subdirectory didn't load it.
In the logs it shows this error when loading Landclaim:
Quote[ERROR] [19:26:01] Java RegisterEvent - Event not found: Events.Player.World.PlayerWorldEditEvent UnityEngine.Debug:LogError(Object) RisingWorld.PluginAPI.PluginEventHandler:OnRegisterEvent(IntPtr, JObject, JString) (at C:/GitLab-Runner/builds/jxpAq3Km/3/jiw-games/rising-world/Assets/Scripts/PluginAPI/PluginEventHandler.cs:260)
The server is running on Windows 11 Pro.
EDIT:
On further investigation, having both mods installed actually results in 2 claim plugins. One is controlled via SHIFT+L and the admin page when you press ESC, and the other is when you press B, and everything's managed from there.
I removed the LandClaim addon and SHIFT+L stopped working, so it seems that the B menu is the World Protection plugin. I'm still not sure which one I like better though TBH, but without the World Protection plugin I can't access the LandClaim Interface.
