How does an Instagram account with 50,000 followers make money?

Depends on what the account is about I'd say.

If you can be seen as some expert in a Niche you could try leveraging it to launch your own products, probably the most work but also the highest return if it resonates well with your audience.

As far as I know:

1. Paid shoutouts from other accounts
2. Sponsorships
3. Monetizing the audience by sending them off the app

I briefly explained the process with Notion. https://bit.ly/50kproject