Found a blog post that gives a quick overview of how to do git via email in general: https://peter.eisentraut.org/blog/2023/05/09/how-to-submit-a-patch-by-email-2023-edition
So at least from my understanding you’d make your changes, email the contents of the patch to the maintainer, and then they’d apply it on their side, do code review, email you comments, etc. until it was in an acceptable state.
There’s also the full kernel development wiki that goes into all the specifics: https://www.kernel.org/doc/html/v4.16/process/howto.html
(I never got through the whole thing)
Out of curiosity, what content are you looking for? Discovery on Lemmy can be a problem, but sometimes the communities are there and even active, just buried.
But may I also suggest searching by Top Day/12-hour/6-hour to see the most active posts. Lemmy’s scaled algorithm still doesn’t get it quite right IMO.