I just started a slideshow in 'old' Photos under Windows 10. Easy and instant - as easy as from Windows Explorer via Picture Tools - except that I don't seem able to change the speed.
A few days ago I made the mistake of accepting a free download of Windows 11. No Picture Tools any more in Explorer. Trying to run a slide show in 'new' Photos, apart from it seeming over-complicated, all I could get was stills.
I have been able to Go Back to Windows 10, and will need a live run-through of an example run from a regular user-defined folder, not somewhere in Pictures, before being convinced Windows 11 has all the functionality and usability of Windows 10.
Is it all about making the operating system more device-independent? Most advice about slideshows seems to relate to moving wallpaper. I don't really need that or Windows on a phone.