Nostalgia is a heck of a drug. There are people who live for it. They're passionate about it to a T.
That's why there's a bunch of people who still use old hardware, old software, play old games, and make new things that work on that old hardware and software. For example, there's a vibrant community making Vic-20 games, even available on cartridges and cassette tape.
Best of all, a percentage (albeit a small percentage) of those people are so young that they weren't around in that era of computing. Still, they keep the hobby alive.
That said, it should be trivial to start a slideshow when the device is idle.
This should be a Solved Task™.
XnView has some neat options (it's not OSS, but it's F) for slideshows. Calling that and loading a slideshow with a terminal command should be trivial. Attach it to a systemd file that pops off after inactivity and you should be golden. That's way more work than it should be. Someone will make it easy enough with Wayland. After all, it's just a bunch of protocols. That's all Wayland is.
