XP Limiter
This mod implements a configurable limit for players' maximum experience level. By default, the limit is set to 250 levels, but you can easily adjust this value - for instance, restrict players to 30 levels. In this case, when a player reaches level 31, their progress automatically resets back to level 30.
The modification must be installed on the server side, while client-side installation is optional. All configuration settings are synchronized between client and server, so users don't need to perform any additional actions for proper functionality.

This gif shows what happens when a player uses the mod without client installation - note how the experience indicator fluctuates between levels 10 and 11.

Here, stable operation with the modification present on the client side is demonstrated - the experience indicator remains reliably fixed at level 10.