NoMenuBlur
NoMenuBlur is a clientside mod that allows you to disable the blur effect in the pause menu that was added in 1.21. The mod also allows you to restore the old in game background, and customize the color of that background. There is also an option to use the new background but without the blur.
Dependencies
Fabric API - Required
YetAnotherConfigLib - Required
ModMenu - Optional
The Config Menu with default settings applied
An example of the menu with blur disabled but with the minecraft default background
You can make your pause menu look however you want (I am not responsible for people judging you)
You can use the blur effect with the custom colors if that's your kind of thing