Nope, that didn't work. Still looking for a fix for the problem.

2022 Mac Mini + Satechi Type C Stand and Hub with SSD + Western Digital 2TB SSD. I set the system up with the SSD as the backup drive for the Time Machine. Worked for several weeks then started giving me: “Disk Not Ejected Properly Eject ‘Backup’ before disconnecting or turning it off”. I tried running first aid. Didn't help - still got the messages. I wouldn't get the messages when I was using the system only when it was sleeping. So after looking through the forum I tried reformatting and first aid again then set the energy settings to “Prevent your Mac from automatically sleeping”, disabled “Put hard disks to sleep” and “set Wake for network access’. I've also started locking the screen instead of putting the system to sleep when I leave it. Seems to be working ok now. Time Machine is running backups and I’m not getting messages so far today.