In the past, when it didn't look like ZFS was going to continue when Oracle closed it down, mm@ forked the man pages and rewrote them in mdoc(7).
While the rewritten man pages had nicer and more symantically rich markup, the divergence causes additional work every time a new feature is imported.
As an example rS337669 imported the large_dnode feature from Linux but missed the man page update (likely because Linux stores the man page in a different location)
There are no changes to the text of the man page, except to correct the chapter markers, and remove a comment about FreeBSD's boot loader not supporting large_blocks (it does now)
Once this is committed, I'll import the large_dnode feature section from ZoL.
The inspiration for this was was the site https://zgrep.org/zfs.html which parses this man page to determine which features are supported by which OSes, and it incorrectly indicates that large_dnode is not supported by 12.0 and 13-current.