You can use other file/media servers than nostr.build and the other few big ones. You just have to have yours added to a whitelist. I think.

I seeee. Is this what people mean by nostr-as-file hosting? It's v likely I'm confused lol. I think this includes no AWS hosting? Self-hosting or something? (I really don't know what's going on, I must stress this some more lolol).

Yes, the notes (on the relays) don't contain the images, the media servers do.