yes and they either become popular because of their usefulness and get organized like firefox/mozilla or they get co-opted by corporations and invariably enshitified like chrome/chromium
Firefox/Mozilla as an example is a bit of a stretch, given the fact that Mozilla Browser/Firefox is originally based on the open-sourced version of Netscape Navigator
There is a very large corpus of FLOSS software out there serving everything from individual itches to whole industries. Any project that is important to someone's bottom line is likely to have paid developers working on it but often alongside hobbyists.
The project I predominately work on is about 90% paid developers but from lots of different companies and organisations. Practically though the developers don't care about the affiliation of the other developers they work with but the ideas and patches they bring to the project.
100% of the open-source software i contributed to was developed by hobbyists so, using that information, you can infer from only that information that only hobbyists can develop open-source software