Lots of successful FOSS projects have no 'elements of capitalism', depending of course on how you define the latter. Same goes for much scientific research, and many other enterprises.
I'd love to be wrong about that.
Also, as in my other comment, it depends on how we define the involvement of capitalism. See my other comment:
Linux absolutely is carried to a large part by companies employing people to work on Linux. Mozilla needs to find income to pay its own employees. All three are slightly different models, but all three make it fairly clear that you can't cut all ties.
As for the "what do you mean" part, "obtaining money via capitalist endeavors related to the project so non-affluent devs can actually afford to work on the project" is probably a good enough definition.
In comparison, Signal is small - and even it can only make it because an extremely affluent person (Brian Acton) carries them. It's not reproducible for larger projects.
It's a society with lots of capitalism, so of course you'll have people involved who are also involved in capitalism; you'll buy your computers from capitalist companies, etc. That doesn't seem meaningful.
So what do you mean?
I mean that projects don't need to be capitalist enterprises. For example, they can run on donations or grants, with volunteer labor, etc.
Of course there are such projects that receive enough in donations from end users to be sustained but not very many; and in the particular case of Linux desktop environments or distributions there is a lot of competition for users and donations of this type. The successful ones I can think of off the top of my head, such as Libre Office and Lichess are "killer applications" with no serious competition in FOSS.