Let's start with: there is no such thing as "Linux" man pages. There's <https://docs.kernel.org> but that only concerns the kernel itself.

How does a particular distribution handle its man pages is up to that distribution. You can browse what is generally considered to be the "standard" set of man pages online: <https://man7.org/linux/man-pages/> or <https://linux.die.net/man/>, but this is a third-party community effort. I've often found minor discrepancies between those resources and what I actually found installed on my system.

Debian does an absolutely amazing job: every executable in every package has to come with a man page, and if there isn't one, the maintainers will at least write a synopsis. You can also read these man pages online: <https://manpages.debian.org>; you get to browse by release, section, you even get translations. Some derivatives (e.g. Ubuntu) will provide their own online browser as well.

But this is where things start to get dicey. Most distributions make heavy use of GNU coreutils, glibc, GCC, etc. Some of these (like GCC) are complex, because the problem domain is complex. On the other hand, coreutils' level of unnecessary complexity is almost byzantine; to cope with that, the GNU project mostly abandoned man pages (these mostly just contain a synopsis) in favour of an in-house "info" system <https://www.gnu.org/software/texinfo/manual/info-stnd/info-s...>, which is basically TeX <https://tug.org> with layers on top.

But not all distros use GNU tools nowadays; e.g. Alpine (actually pretty popular, thanks to the Docker ecosystem) uses busybox and musl libc. However for some reason Alpine not only does not provide an online man page browser, but requires installing a meta-package to add the man pages to your system. The differences between GNU and busybox+musl are non-trivial (and not unlike GNU vs BSD).

You can blame the Linux ecosystem fragmentation, and you would be correct to point out there are three popular BSDs, each with its own goals and little quirks. My final point is about the quality of the documentation. Compare coreutils chmod(1) <https://linux.die.net/man/1/chmod> and OpenBSD chmod(1) <https://man.openbsd.org/chmod.1>. The former is a brief, dense, and intimidating wall of text that expects you to immediately grasp what "ugoa" or "rwxXst" stand for; you will only find out that the tool manages file access permissions once you dig through the third paragraph; the text concludes by referring you to "info coreutils aqchmod invocationaq". By contrast, OpenBSD's man page has a clear introduction, then paces you through explaining the basic; goes into detail over the octal and symbolic representations (with pretty tables); warns you about a common mistake; has several examples with explanations (including equivalences between octal and symbolic forms); and concludes by referring you to the POSIX standards.

Best of it, you can expect the same high standard of quality throughout the entire base system, from user commands to device drivers and kernel internals.