catalog on EHD won't back up

hi all,

I recently updated to Mac Catalina and PSE 2020.  I keep my files and catalog on the EHD, but the program is on my computer. When I try to make an incremental back up and start by loaded the last back up, once I click on the .tly file,it just keeps thinking and thinking and never gets anywhere.

I have been told that i can't use an EHD because it is too slow communicating with the computer, but many people on this board have said otherwise.  I have too many files to keep on my hard drive - how can I make the catalog back up? Do I make a separate backup catalog with each incremental back up, or should I overwrite on a previous one?  It does load up OK.

thanks,

Sharon