AFAIK the Linux Kernel doesn't have a single source of truth.
Of course some (many) people are using forks, but all sync directly or indirectly with this dude's version.
Linux kernel dev branch single source of truth is https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
The stable branches have their single source of truth repositories, too.
There is a single source of truth for a particular version of Linux.
A few days ago I read about the multiple Linux distributions that all have their fork with special patches etc. pp.