Mac OS Ventura changing wallpaper based on "Photos" app

Hello. After reading some older discussions re the same or similar topic I checked all the good recommendations etc.

My issue: MBP (M1 Pro Chip); Photos library > 1 TB = on external HDD (connected directly to MBP via USB-C).

Library is set as "System Library" in Photos settings. I am using an external Monitor via HDMI and the built-in 14" Laptop Monitor. For both I have selected different Photos sources for the respective wallpaper (e.g. for one monitor "all photos" and for the other one "Albums"). Both settings selections are set to "auto-rotate" and e.g. 5 minutes frequency and "randomly".

So far so good - the result is however disappointing: the system will pick some images from the various selections but - as example - show only 5 different images from "Albums" with 12000+ images in total. Same with the other selection.

Was already running "repair" function on the library which did not change anything.

Anyone a good hint or idea how to get this fixed or where to start investigating?

Honestly - bit lost since I believe I have used all the correct settings and OS functions as explained on the Apple support website.

Thanks in advance for any help.

Robert