Cmd + Tab doesn't bring the main window to front
When I use Command+Tab to navigate between programs, I have to hide all open programs to see Illustrator's interface. The open palettes will display, but not the the document window, toolbar, application bar. When I try to hide Illustrator, only the palettes respond. Illustrator is generally sluggish with High Sierra.

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Related to this report:
Cmd + Tab app switching forcibly keeps Illustrator in focus
http://illustrator.uservoice.com/forums/601447/suggestions/45058171 -
Minty commented
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, i.e.: 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.