Same problem. Bought Mac Mini M1 and connect an external hard disk (Crucial 1To SSD). After a couple of seconds, pop up about "Disk Not Ejected Properly" appears and others follow... (tips: use "killall NotificationCenter" in terminal to close all notifications in one shoot)
On my old iMac mid2011 with High Sierra, no problem, the same external disk works fine...
rparmantier
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