I work with switching setups on my macbook, sometimes without an external screen, sometimes i move to my home office and plug in a bigger display.

When indesign is opened and a file is opened, you cant do that without having to save and reopen the document. Because whenever you attach or detach a display - the main artboard / window with pages turns completely grey / invisble and you cant see anything anymore, but you can hover the elements.

Switching to "Overprint Preview" brings back the visibility, switching it off makes the pages invisible again. Same with "Preview on CPU".
So this seems to be a problem with the GPU Viewing.

I use InDesign 20.4.1 but i have this happen since 1-2 years now. Before there was never a problem when switching displays / setups....

Macbook Pro M1 16" 2021
External Display: Alienware AW3423DWF 3440x1440

Please check and fix - thank you very much!