Are video files able to play in full with Photos slideshows anymore?

I've been making slideshows in Photos for years but had an older Macbook Pro and hadn't updated it in a long time. Using a new 2020 Pro now and I've been trying to create a slideshow but the video files are playing as if they're a still photo. When a video comes on, it plays a second of the clip only. I did a search on this and I know it's been asked a couple times but there weren't any answers except for one that said that only the "classic" slideshow option would now allow play full length videos so I tried that but it still truncates the videos. I haven't rendered a video yet and have only previewed so I don't know if it just can't preview but I can't imagine that would solve anything as the preview option previews the videos to the time duration that one sets. Anyway, if anyone knows a solution, it would be greatly appreciated. If they've limited the ability for Photos to handle slideshow capabilities in this way, is there a good alternative besides iMovie? I don't feel like having to manually create all those transitions and things like Ken Burns effects on every photo file. Thanks.