Shutup Experimental Settings! Mod 1.18.1/1.16.5 is a forge part of a mod called Disable Custom Worlds Advice. It stops Experimental Features advice from appearing.

Have you ever felt annoyed when the Experimental Feature advice keeps appearing on Minecraft screen? Normally, when you make or load a world using some custom dimensions or world settings, that advice keeps popping up. Because this causes some players to feel annoyed, a World Gen mod was made to stop it, which is called Shutup Experimental Settings! If the screen is annoying you, then you should use that mod. By installing it, the advice of Experiment Feature will not be visible on the screen anymore.
The mod is free to install and easy to launch in the game. However, for its operation, you have to install Minecraft Forge first.