There are many of us who flip back and forth easily between Windows and Mac.
Avid is pretty much the same on both platforms. Yes you may have to learn to deal with command instead of control key use, but the program itself is identical.
I usually found my first day back in Mac was a bit of a “oh ya…im on Mac…can’t hit that key” but doesn’t take long to get in the groove. The a week later i’m back on Windows, going “oh ya…i’m on windows…can’t hit that key”…rinse and repeat.
I cant speak to what a big hollywood post company would prefer, but If you are just getting started, i wouldn’t worry about it. Learn the program, and go on from there. The only thing that would hold you back is if you went in for an interview and said “i only work on Windows…and I refuse to work on Mac (or vice versa) If you want the job, you will work on what ever platform they have.
Glenn