I have a new MacBook Pro. I just downloaded several free HD backgrounds (about 50+)from the internet and placed in a folder. I added the folder to the Desktop & Screen Saver app.
All of the new images are .jpg files. But when I added the folder, only 10 of the images display and are used as the background.
I researched online and tried setting "Change picture" to every 5 seconds to try and "force" cycling through all of the pictures -- this didn't work.
I looked at file details --- thee only difference is the date of the files. The folder is only displaying files I added over a month ago. (Also downloaded from the web, same websites.)
I am not using iCloud Drive (I use Google for backup.)