I don't think any microphones should be cut off. How a candidate responds to interruptions and challenges is part of the debate. What will they do when they are pushed a bit and have unfriendly questions (for Democrats).
Otherwise, we might as well just have each of them do separate press conferences. If the microphones could be turned off, the damn moderators would be cutting off the one they don't like and letting the letting the other speak. It would not be equitable.
The main criticism I heard of Trump was that he should have let Biden talk as Biden was spouting a bunch of talking points some of which were publicly disproven. I can see that, but I think Trump needed to push Biden to some extent. Trump went overboard a little bit, but Trump will do that. Biden didn't handle it well. He was mostly falling back on talking points and trying to throw mud at Trump. Trump could have had better responses at points. Someone like Ted Cruz would have thrown out a lot more good facts and information, but he isn't Trump and Trump did get plenty of hits in.
I don't think Biden won the debate at all, but I don't know if I would say Trump won. I want to say he did, but I am inclined that direction anyway.