Photos Library on external SSD - cannot eject the external SSD after upgrading to Catalina

Hi,

with Mojave, I used to keep the System Photos Library on an external SSD, with no iCloud Photo activated, but only Shared Albums, and I was able to unmount the external SSD without any issue at any time after closing the Photos app.

After upgrading to Catalina, and after the completion of the automatic re-organization of the photos made by the new Photos app in Catalina, I now notice that my external SSD cannot be unmounted, unless I log out of my account, or I force the processes like photolibraryd, etc.. to quit in Activity Monitor, or I switch off the Mac.

This is quite uncomfortable to me, as I need and have to be free to unmount the external SSD when I move around with my MacBook. Moreover, in case I force the ejection (by mistake or for any other reason), when I mount again the external SSD and launch Photos app, it tells me that the Library has to be repaired, taking lot of time, and one time it even happened to end with error 1000 (which fortunately I solved by double clicking directly on the Library file instead of selecting it after option-click on the Photo icon in the Dock).

I can confirm that the issue doesn't occur at all if the same Library on the external SSD is not designated as the System Library.

I also tried to create a brand new Photos Library with just couple of pictures inside on the internal drive and moved to the external SSD as per Apple’s instruction (as I did first long time ago in El Capitan), and I can unmount the external SSD until I designate it as the System Library.

I would like to thank in advance who can help me on this matter.

Marco