The hier manual page currently conforms to version 2.3 of the Filesystem Hierarchy Standard. In CONFORMING TO, it states this and includes a link to the Version 2.3 URL. However, the FHS specification was updated to 3.0 five years ago. The new specification appears to live at https://refspecs.linuxfoundation.org/fhs.shtml.
I'd like to take a look and provide a patch to update the manual page for filesystem hierarchy. I'll ask at the mailing list as well.
Since Thomas Piekarski's patch in https://lore.kernel.org/linux-man/c1c52c68-5fa1-246f-06c6-2bbe647c65ca@deloquencia.de/ has been applied, I think this bug can be closed, so I am doing so. Thanks, Thomas and Gary.