I submitted feedback over it but, aside from the over-reliance on rounded corners, and making pills and buttons hard to separate, the single worst change is that you can't see the latest commit status from the repo screen. Instead, you get the commit hash, and have to click a tiny ellipsis button to get the commit message and the status indicator.
When I'm browsing on github and not using git directly, the commit short-hash is the last thing I care about. You cannot see if your default branch has passed CI/status checks now. Those things should be first class citizens, that's why we put status badges all at the top of our readmes to make that info more visible with what we have.
It follows the trend of designing with lower information density. This trend IMO is not appropriate for developer tools.