Can’t change the playback speed or display pictures from Photo app post update

I also have this issue- although slightly different. The issue seems to be Apple does offer a default value that can be tweaked or an adjustment for a on the fly slide show option -( select a bunch of photos and click slideshow), nor this issue. When you create a custom slideshow, you get this option for slide speed. So something is corrupted during the upgrade. Apple, every slideshow should have an adjustable slide speed 🤷‍♂️

I just called Apple support and talked to a senior advisor, I spent one hour to help him see the issue on his iPhone, he agreed that there are lots of issues with the Airplay and slideshow.

But I discovered while on the phone that if you tap one image from Photos and go to the left Arrow the Airplay option is there, and once you connect to a smart TV, then select slide show form the meatball menu - 3 dots- on the left and play slideshow, strangely enough all the photos after that one you tapped on. You can do the same without Airplay, just on your mobile device. The main thing is do not select "select" just tap on one photo and gets a slideshow, but it is very strange it crops on its own and plays 3 photos in one slide, I don't like this, but hopefully the senior tech he said he's escalating the issue and within 24 hours. Another option if you want to do a slide show on your smart TV is screen mirroring.