This is a direct result of 24w09a's changes and did not happen previously; all of these were transparent in prior versions.
For the Game Menu (Esc), this is particularly inconvenient as it forbids the viewing of anything happening in-game, unlike previously, which can have a major impact if pausing due to an imminent threat (e.g. close range creeper) or in multiplayer.
Affected menu screens
Game Menu (pause)
Options
Open to LAN
Advancements
"Do you want to open this link...?"
Skin Customization
Controls
Credits and Attribution
"Are you sure you want to quit?" (via title screen button after death)
Command blocks, structure blocks and jigsaw blocks are also affected as a result of MC-268956, and signs and hanging signs are affected as a result of MC-269077.
How to fix
Introduce a new, dedicated background texture file for the above menus. It would only be present in the default textures; neither Programmer Art nor High Contrast would change it, so it can be left out of both resource packs as to fall back to the default.
Linked issues
is duplicated by 5
relates to 2
Attachments
Comments

Also affected to signs editing backgrounds for some unknown reasons