I think the issue you’re running into is that you’re using the free level of nostr:npub1nxy4qpqnld6kmpphjykvx2lqwvxmuxluddwjamm4nc29ds3elyzsm5avr7 which limits your file size per upload.
If you’re not aware, Nostr is different than the social media platforms you’ve used because it’s not a company and everything here is built and run in a decentralized way. Media hosting isn’t native to the protocol, so there are services that provide those features, which are run by independent teams.
Yes, there’s a subscription cost, but I find it worth paying for all the features it has. You can also recover the cost over time with zaps. 😉