It wasn’t mentioned in the list, but I like Photoview; it uses your existing file structure (rather than its own structure or a database), works with read-only access, accepts external syncing like Syncthing, and can handle multiple users. Not sure how it compares on features, but I just wanted something basic anyways, so I’m happy with it.

Let’s build a ship out of it.

For KeePassXC itself, no. I use KeePassium on iOS, which seems to be compatible with most of KeePassXC’s features.

If you’re using KeePassXC, it supports them right now. I’m using them on a few websites with the browser extension. Your mileage may vary, of course.