redxef
%0.2 of 50 is 0.1 you are talking about %20.
Honestly I thought you were going to bitch about them separating your metadata from the photos and you then having to remerge them with a special tool to get them to work with any other program.
You can even go further and install syncthing, I'd never want to go back.
In theorey lots of people recommend having everything in a single docker-compose file for easier transfer and separation, though I have so much running, that it's grouped by purpose. One of those is data storage. So I have a single server with all the databases (as far as compatibility goes). I would like to some day have a highly available postgres cluster with automatic failover and failback. But that needs a lot of testing and I'm no postgres admin, so also a lot of time to research how to do it properly.
Honestly, alpine is a great distro, but not really something I would recommend for a beginner. There is less documentation and troubleshooting guides out there tailored to this distro than for example debian or ubuntu.
I would either recommend using Debian or a derivative of that if they want to get their toes wet. Alternatively a complete solution with GUI tools for if they just want to start using their own stuff now.