Yes, that’s how I use it. It has access to a read only bind mount of my photo directory. The ML doesn’t write exif data to the images, just keeps that in its database.
I see you have a bunch of good answers now, so I’ll ask; if you are comfortable self hosting, why not consider a VPS? Yes it can be a little bit of maintenance, but it’s very minimal and you get far more flexibility and the ability to further develop those selfhosting chops.
This is signal detection theory combined with an arms race that keeps the problem hard. You cannot block scrapers without blocking people, and you cannot inconvenience bots without also inconveniencing readers. You might figure something clever out temporarily, but eventually this truism will resurface. Excuse me while I solve a few more captchas.
I use both as well. They server different purposes. When my wife wants to take a quick scan of a paper document and archive it instantly, or have pictures auto-upload, or open and edit a document we worked on a year ago, all on her IPhone, the Nextcloud client works great and really has no competition in the iOS world. When I want to keep the files in my home directory, including some big, regularly changing files, instantly synced between computers and hosted VMs, Syncthing is amazing. I also add Syncthing shares as an external source in Nextcloud, so I can open those files via the web. As others have said, Nextcloud works fine, provided you don’t start installing all sorts of “apps” you don’t need -stick to the basics.