I know donations are an option, but I don’t think long term donations will be sustainable. Most users will never donate. I don't think that they are not sustainable. If everything works out to be a properly federated network that is made up out of a lot of small to medium sized instances I think that it would be sustainable. Hosting costs should actually not be too expensive. You don't end up with millions of users on a single instance causing it to have massive load. And users are generally more willing to contribute financially if they get the feeling of using a platform that reflects their values and is run with their interest in mind.

If you have ever browsed sites like questionablecontent.net, you may have noticed that they have a privately hosted ad server where people can reach out to Jeph and buy ads for his site.

This is a fairly rare occurrence as the requirements for the ads that he approves are pretty strict from what I understand and he's not just going to hawk the latest caffeinated Seltzer vitamin water blend to his followers.

That being said there are a lot of self hosted ad platforms that can be easily monetized and allow the site owner to dictate exactly how intrusive the ads are where the ads are coming from and to ensure that the ads effectively blend into their site design.

But a more realistic approach would be to ask users to pay an annual fee or something.

If I knew that the community was fairly strong and robust I wouldn't mind paying $10 a year or something to keep my community vibrant and strong, or rather than going with a fixed annual amount if they were to put out a donation drive the way Wikipedia does then I might be tempted to throw a little cash when I'm feeling flush.

like the rest of the Fediverse: through ingeniosity, community and self-organization!

(understanding "make money" as "pay for its infrastructure and maybe for some dev and other of the essential work now ran by volunteers" not as "profit")

There's also the option if user-owned cooperative (like social.coop) - https://blog.opencollective.com/social-coop-a-cooperative-decentralized-social-network/

There are also some masto instances that have their own lemmy instances, funded through their existing funding structures - https://merveilles.town/about