This resourcepack changes the splash text (next to the Minecraft logo on the main menu) to be like the default Minecraft 1.21 splashes. This is because some mods might change it to be their usernames (or something else), which some people (like myself) don't want when making modpacks etc.
The installation is just like every resourcepack, but make sure to put this pack up at the top of your list with all active resourcepacks. This is to make sure none of the other resourcepacks change the splashes.