It is not necessarily monetary or even transactional form of support. Reciprocity builds relationships.

Not necessarily even code contributions. It could be professional networking. It is a bit different if the person is not a stranger.

The effort to setup donations is almost always more trouble than the donations that result are worth. Better spent looking for a job, or working on a commercial project that will make money. People simply don't donate to open source projects at a level that matters.

I've been working on Open Source software for 30+ years. There's no money in it, if your idea for making money is "accept donations". I don't like it, but it's a fact. If you want to make money, you have to make something that isn't free (and even then, if you give away the most valuable parts, as in "open core" licensing, you probably still won't make enough money to make the development worth it).

When I was young and driven by idealism and optimism, I assumed that with enough users I'd be able to ring the cash register somehow. Turns out not so much. We got the users, the money never came. There are a few outliers, but there probably aren't a lot of opportunities to found a Red Hat today.