I am using Adobe Elements 2021version 19.0 on a recently purchased iMac 27" 2020. I have imported about 80,000 photos from a number of subfolder on my Macintosh HD. Sometimes (and sometimes not) a second Macintosh HD folder shows up in the folder tree and sometimes (and sometimes not) it has a number behind it and sometimes (and sometimes not) it and all subfolders are greyed out. When I try to view a single photo it is often of low quality and sometimes (and sometimes not) it says the photo is not connected and it can't find the photo. Sometimes this problem goes away by itself and sometimes doing a catalogue optimization solves it, but sometimes it doesn't. When I say "sometimes" I mean sufficiently often that Elements is essentially unusable becase I don't know whether it's going to work or not.