If you are unable to use Adobe Illustrator Or Can't go full screen on mac then I have shared How to use Adobe illustrator on full-screen mode on Mac OS Big Sur.
As I am totally New to Mac and which using Adobe Illustrator I found the problem in which it was not going Full Screen.
So To go Fullscreen first you have to double-tap the doc. After that click on auto-hide.
Now On Adobe Illustrator tap on F key and it will maximize the window.
In This way I was able to use Adobe Illustrator in Full Screen.