I was looking at Borg but that's one of the tools where it seems like I need the entire replicated copy of the dataset locally to add more. I believe Borg can open a view into previous versions of the data, so it's technically append only, but I'd find that process tedious.
These are a couple TB and mostly photos I've taken. I'd like to be able to browse and edit at some point, but my primary concern right now is keeping a copy of everything.