Our CI tests run with mongo 3.7, so you can go as old as that.
@PitaJ i mean categories
The only things not in the database that is can think of are uploads, which the docs you linked describe how to back up before an upgrade.
A user submitted image gallery where you can comment and rate pictures. <sigh> hopefully someday.
@cani Yes it runs NodeJS and I can only upload files.
@psychobunny Oh I see, thanks 🙂