I’ve been part of workshops run by key contributors, as well as seen consultants brought in to try to optimise code using their open source code. There are a lot of ways, but they usually aren’t as direct as “normal” employment.

There’s also another category where you get hired by a company using your code to help drive and prioritise enterprise features in the project. I’ve seen plenty of internal forks of big open source projects where contributors are actively working and trying to upstream the internal development.