Why must I "force quit" to close Photos after updating to Mojave ?? 13" MBP(mid 2012) Mojave

Thanks for your help. I replaced my dysfunctional Photos 4.0 libraries with backups from Photos 3.0. Opened with Photos 4.0 and let them each convert to 4.0 format. Logged out of my account. Set up a new account and opened Photos 4.0 in new account. Seemed to work fine. Logged out of new account and back into my main account. Now everything seems to be working fine. Not sure whether the replacement and conversion with backups or the switching of accounts resolved the problem, but something did and I have spent

Thanks, Leonie. I have let the "closing" run for several hours on a relatively small Photos library, but it doesn't close. So I have to "force quit" Photos. That sometimes appears to damage the library so it can neither open or be repaired. I have over 40 separate Photos libraries for my photo storage, so letting each one of them run overnight in order to close even a relatively small library file doesn't seem like a satisfactory solution. It appears that the updating to Mojave changed the internal HD (not an SSD) on which my photo libraries were stored from Mac OS Extended (Journaled) to APFS formatting. I didn't think that it would do that without permission. I am wondering whether that reformatting has caused corruption of my Photos libraries. Thanks again.

Thanks for your help Pedro D. The failure of Photos 4.0 to close some libraries appears to persist with multiple Photos libraries. Also when booted up normally or in Safe Mode. And after reinstalling a newly downloaded Mojave. I'm suspecting a bug in the updating of the Photos 3.0 libraries and have reported it to Apple.

I haven't yet tried creating a different user account to determine if the "closing the library" problem persists.

Thanks again.

I have just reported this to Apple. Thanks for your help, Leonie.

too much frustrating time working on it. Next time I'll wait longer before upgrading to a new OS!