-yes, for parts influenced by the downpipe, in this case anything drivetrain related.
-yes, if the CEL isn't cleared and a decent mechanic can tell by tool marks on the bolts that they've been removed and reinstalled. If your whole exhaust is dirty, but the downpipe is nice and clean... dead...
Never seen that one before. Maybe look on a BMW forum if it's a thing or if it's just a random one in a million failure. Usually when a part like that fails it was because of faulty construction at the part assembly and it's just a matter of time.
They're both underrated. Stock for stock there's about a 40 wheel horsepower difference. But torque is virtually the same. The difference is negligible. Bigger difference is the suspension feel. I forgot which track it was, but the '21 lapped significantly faster than a '20.
I haven't had any...
Reading along every now and then, rolling my eyes, and moving on.. Tired of arguing with paranoid morons. They bring you down to their level and beat you with experience.
So I'm just staying out of it.