So I think I figured out how to show all of the photos in the album, not just a select few, and to keep it from cropping them all weird. So what you need to do is go into the Photo Frame settings and select "Show Pairs" on the portrait option and then select "Live albums only" under personal photo curation and it will show all of the photos without cropping them. It also will show two portrait photos side by side instead of oddly cutting them in half to make them fit one at a time. After changing hose settings I haven't had any issues.
Hope it works for you!
It looks like we have come to a solution so I'm going to be locking this thread. If you have any other concerns or questions, please feel free to create a new thread.
Have a great day.
That did the trick... Regular 16:9 photos are fine, and now the medium format slides present properly, too. Thanks so much for your help, this is to facilitate the gift of a Google Nest Hub and it was going to be a bunch more work if I had to crop each and every one of the slides I've scanned.