Thanks, but I’m an idiot. I dug around a little and realized I was low on disk space and running a badly outdated version. All good now.

Do some searches on “kiosk” software. That’s the general term of art for machines that are intended to run a single program/interface. As for distros, you’ll want something light and easy to maintain, ideally with automatic updates. Debian’s an obvious pick. Alpine could be great for something like this. Gentoo could be awesome too, but there’s a serious learning curve involved.