You can configure storage paths. That way, you can direct tags to be stored in a specific folder.

You can then get the files for the accountant from your file system.

Some apps have breaking changes. If you can restore a complete backup when that occurs, you can recover. Immich is famous for its breaking changes

I would recommend to avoid Scaleway. They simply lost part of my files in the first week. Were very unresponsive and in the end could not recover. Pretty much everything you are hoping to never encounter with a storage provider.

I have had a lot of fun setting up Unraid. It has everything you are looking for. It does cost some money to start, but was very much worth it to me.