For what it's worth--when I had an 8GB Air, decoding video in a browser didn't seem to really impact performance. Plugging in an external monitor, though, was not a fun time.
I have a 32Gb M1 Pro as a work laptop and connecting a retina 4K external display is not a fun experience for me either. It was very surprising to see it fail to maintain 60fps in the OS’ own animations.
