I use a 49" Samsung monitor that does 4k and like you mentioned my Intel work macbook pro is constantly spinning fans/hot. The M1 I honestly haven't noticed it making any noise while plugged into it. It also runs a lot better, less graphic glitches and weirdness. I don't like having to use my work mbp at all anymore.
I had an M1 MBA and it ran my 4k monitor fine. I would use it and the laptop screen at the same time. Great machine. I ended up giving it to my wife and getting an M1 MBP because I needed more than 16gb RAM for my workflows.
