Framerate in game menu is slightly lower than when the game is unpaused in empty world

Not sure what could be causing this - the difference seems more pronounced in the 1.20.5 development versions, perhaps due to the game using a tiled texture for the background as opposed to a darkening. This is still the case if blur is disabled.

Performance improvements to be made here could include stretching the background texture instead of tiling it (perhaps through a resource pack option), meaning less textures need to be rendered, as well as potentially expanding the default size of the button widget textures, as I believe some repeat at this scale (see also MC-269152).