Media such as photos and videos must be hosted somewhere. Big tech platforms make this easy by building it into their servers, paid for by advertising dollars.

Nostr doesn't have that. Amethyst doesn't run a media hosting server. Most clients don't. Primal does, but there may be limitations on the type of media and file size.

A lot of other clients use nostr.build to host media by default, and you can upload files there for free up to 50MB. You can also go to their site and upload there directly. You will receive a URL you can paste into your note in your Nostr client of choice and any client that can render the media in their feed will do so for anyone who sees your post.