The main options that I'm aware of are: selling support (RedHat), donations (I can't recall examples but they do exist), open-core (GitLab), and paid hosting (WordPress). In the past, there was also the option of selling physical media (which the FSF did for GNU projects, for instance) but that's been killed by the Internet.
All of these models are very hard to get working (e.g. the donations model requires that you have a very large number of people interested in your work who are generous with their money, kind of like Twitch streaming), but they can work. They're not an option for the majority of programmers, though.
All of these models are very hard to get working (e.g. the donations model requires that you have a very large number of people interested in your work who are generous with their money, kind of like Twitch streaming), but they can work. They're not an option for the majority of programmers, though.