Anyone have tips for a parent-teacher conference now that we can see the class in Zoom school? Would it be OK to provide feedback to the teacher on the teaching? Things that work/don't work for my child. Not sure how far to push this to a critique. Thoughts?

I wouldn't ever be directly critical unless it was really, really, really bad. Better to lead with the positive -- Jane responds amazingly well when you do X -- wondering if you can do more of that? I noticed that Joe has really great days when you do Y. Can that be a regular part of the classes? I would also check in with other parents because if there's something that bothers all of you you can send a consistent message. They will listen and respond.
I agree. I don't love one of my child's teachers and thought about e-mailing the principal, but decided not to. I think your approach is right, emphasize what is working and ask for more of that.