Immich, a self-hosted app for photo and video backup/viewing now has support for already existing libraries in a read-only mode.
I have not tested this yet, but this was actually the missing feature I was waiting for. So if you have not looked into it for a while, maybe now is a good time to do so.
Immich is one of the foss projects that everyone should contribute money/time on it. It is great, stable and blazing fast.