Possibly of interest to some of you: I am using the Radxa Zero (both, 1st generation Zero and Zero 3W) to run a digital photo frame application (01memories), which I developed myself.
The application is written in Python and uses the Kivy framework. It is not specifically tailored to the Radxa, but the application and the Zero make a very good fit.
Due to the impressive computing power, GPU acceleration and plenty of RAM, photos do not have to be pre-processed, but can be retrieved online from different sources, displayed and processed on-the-fly. Due to the small form factor, the Radxa Zero can also be directly integrated into a frame.
Here is a photo of the frame, which I built:
Alternatively, you can just hook the Zero to your home TV. In combination with Home Assistant, a motion and IR sensor, you can do amazing things.
I would be very much interested in feedback in case you decided to give it a try.