This is happening to me too and is causing a huge problem for me as a photographer -- I keep all my photographs on an external 5Tb Seagate drive, and when I'm running Lightroom, having the disc spontaneously "improperly ejected" really wreaks havoc in my lightroom catalogs. It only happens on my new MacBook Pro laptop running Monterrey and NEVER happens with the same hard drive on the iMac running Big Sur.