Yes. The Apple TV app has evolved into something quite a bit different than the old video library. It’s all about purchased and streaming content. I’m not even sure how you are getting videos into it; though I’d guess it’s probably by syncing with iTunes on a computer. There is no slideshow like feature, and no way to trick it into one.
I suppose you could sync the (short?) video clips to Music instead. Add them to a playlist and use the shuffle and replay buttons to play them randomly and continuously. But this is also a stop gap, and unlikely to be satisfying.
Like most of the time when an Apple app doesn’t do the job, it’s best to look for a third party app. There are several audio/video library/player apps out there. You can use NPlayer similar to how I just described using Music (random continuous play of a playlist). There may be others with real video slideshow features, but I’m not familiar with any of them.
There are probably several slideshow/presentation apps that will do what you want. Also not familiar with them.
But as for Apple’s apps. The only thing that will currently mix photos and videos into a slideshow is Photos.
You could make movie combining your photos and videos using the Movie app, or something similar using Keynote, but they would not be random, and would not let you easily add more photos/movies after the fact.
Good luck.
