I’m also having issues with my external display (HP 24f Ultraslim Full HD, 23.8 inches) while using Microsoft Remote Desktop App. After waking up my MacBook Air 2020 M1 from sleep mode, the external display will take a few seconds to turn on (which is fine) but some times the app will not allow me to use and view the full screen mode (the second screen will only show the Big Sur desktop). I tried to exit and open the full screen mode but the only thing that worked is restarting my computer. I have installed the latest firmware (11.3) so I'm not sure why I'm having this issue.