GitHub: They keep 6%. With 3% for CC fees and 3% for GitHub. [1]
Patreon: Varies a bit more. Patreon takes 8%, unless they have been on the platform since before the 2019 change and are still on the 5% plan. And payment processing depends on size. Under $3 is 5% and $0.10 per transaction. Over is 2.9% and $0.30 per transaction. And more if PayPal or Venmo in not USD.
[2]
So the split seems much better on GitHub. But the conditions are a bit different for using the platforms, and you can get perks on Patreon which you may not be able to get on GitHub. I can't remember who / which project but I believe I saw one that said something about a difference in taxes / VAT and not being able to give some of the perks on GitHub because of it. Cannot find it right now though.
