Checkin history of apple source code? https://opensource.apple.com
I see apple source code can be browsed on line. Is there a git repo in which checkin history can be viewed?
No, Apple just publishes the source code as a snapshot with each release of macOS. The dev repositories aren‘t public.
If you want to propose changes regarding the published code (e.g. porting a Linux system call into the Darwin/xnu kernel), use https://feedbackassistant.apple.com/