Just experienced this issue this morning when I went to wake my M1 Mac mini from sleep. The only change between now and the last week was that I plugged in my Drobo via USB3 yesterday. I have a 4K display plugged in via HDMI, as well as an Apple Thunderbolt Cinema Display plugged in via a USB-C to Thunderbolt adapter. The other day, the Thunderbolt display didn't wake. In both cases, the only solution has been to restart the Mac.