You can contribute that way. (Or with money, for instance.) And good on you if you do. (If you contribute in a way that’s actually beneficial, at least. I don’t mean to accuse you or anyone in particular, but of course there are low-effort PRs and such.) But it would be pretty antithetical to the spirit of FOSS to deny you the use of the software or access to the source code if you don’t. Which is part of the beauty.