It’s not you or your setup. I experience the same behavior. Tried with and without Private Relay, residential and commercial ISPs at different locations, and more to debug it. Same results.
I think GitHub has just gotten so aggressive with their rate limit policies that it’s straight up incompatible with their own product. The charitable interpretation is that they aren’t keeping good track of how many requests each page actually performs in order to calibrate rate limiting.
On the other side of the coin, they also punish people who have slow connections. The acceptable speed for downloading from github on my connection is 90k/sec. No more, no less. Something prevents the rate from being higher (probably Github), and if the rate drops any lower for any length of time, the connection will suddenly abort right in the middle of the download. Since the dumpster fire that is git doesn't support resume, welcome to hell. If I didn't have a fast server elsewhere to git to then zip up and re-download, I'd be screwed.
I think GitHub has just gotten so aggressive with their rate limit policies that it’s straight up incompatible with their own product. The charitable interpretation is that they aren’t keeping good track of how many requests each page actually performs in order to calibrate rate limiting.