Arch wiki is far better than most man pages. I've referred to Arch for my own non-Arch systems and when building Yocto systems. Most Arch info applies.

In the ancient days I used TLDP to learn about Linux stuff. Arch wiki is now the best doc. The actual shipped documentation on most Linux stuff is usually terrible.

GNU coreutils have man pages that are correct and list all the flags at least, but suffer from GNU jargonisms and usually a lack of any concise overview or example sections. Most man pages are a very short description of what the program does, and an alphabetic list of flags. For something as versatile and important as dd the description reads only "Copy a file, converting and formatting according to the operands" and there's not even one example of a full dd command given. Yes, you can figure it out from the man page, but it's like an 80s reference, not good documentation.

man pages for util-linux are my go-to example for bad documentation. Dense, require a lot of implicit knowledge of concepts, make references to 90s or 80s technology that are now neither relevant nor understandable to most users.

Plenty of other projects have typical documentation written by engineers for other engineers who already know this. man pipewire leaves you completely in the dark as to what the thing even does.

Credit to systemd, that documentation is actually comprehensive and useful.