This is anecdotal, but my last “corporate job” was the closest to thing to shrink-wrapped software, even though it was a SaaS. Every release was meticulously documented. Any public facing UI or API change was approved the appropriate teams.
This is similar to macOS, Windows, or even FreeBSD releases. I haven’t seen any Linux distribution that has such comprehensively coordinated releases. Between systemd and the Linux kernel, I’m not sure it would be possible.
Many distros have good documentation, but, in my experience, far too often the bulk of it is in out of date wikis or forums. Perhaps this is out of date thinking and I’ve missed the train in the past 10 years.
As a counterpoint, OpenWRT has been good, but their main “product”, imho, is LuCI. Lower level issues often require vendor specific forums.