A slideshow app that can randomly display between photos and short videos (e.g. gifs) together in the same folder and allow changing display duration for each.
Paid or free. Long as it's cheap and trustworthy. Will be for personal use only. I suppose something like this needs to be flexible with formats (and sizes of photos?) but if not, formats need to be readily accessible.
Edit: I found an app on play store called Simple Gallery by creator Simple Mobile Tools. Has pics, vids, duration per slide, random, etc. So far has worked for me but without some of the aforementioned nuances. Preliminary searches on F-droid did not find much in ways of slideshows capabilities but perhaps someone else will have better luck.