Just moved to an iMac M1 running Big Sur. Using cmd-Tab to switch between Photoshop (or any app) to Illustrator 25.3.1 doesn't bring the main window to the front- it's hidden behind Photoshop.

Have checked with other apps- all seem to behave as expected, ie: cmd-Tab brings all their interface to the front. It appears to be only Illustrator that moves floating palettes to the front but not the main document window.