I have a basic understanding of Grafana since we use it at work. It definitely fits the question, but it’s also very much overkill for my purposes - maybe not in the range of features, but definitely in scope.

Your mention of dockcheck.sh is gold! Someone else mentioned diun, but I think this shell script is even better. As long as there’s a simple way to determine which containers use outdated images, I’m good. The metrics part can be solved with a tool like Beszel or I can whip something up myself if I don’t find anything good enough.