How to switch older Photos version on Catalina to 'Shared' library for family-shared iCloud photos?

recent versions of photos have a toggle at the top that allows a choice of "personal", "shared" or "both" libraries. older versions of photos (5.0 on Catalina) do not have the toggle.

i was using an older mac running Catalina dedicated to a continuous slide show of my 22,000+ photos stored on icloud. i have enough storage on the mac to download originals from icloud to create the slideshow.

things went sideways when i set up family sharing it created a new library named "personal" that only contains the photos created since i set up family sharing (50+). my 22,000+ photos are now contained in the "shared" library. the older photos version on the older mac running Catalina only recognizes the "personal" library.

i need to find a way to make the older version of photos switch to the "shared" library so i can resume showing the 22,000+ photos in a slideshow. i tried turning off family sharing but that doesn't seem to solve the problem.

[Re-Titled by Moderator]

Original Title: sharing icloud photos