Manpage for zpool does not contain "zpool status -D" but it works even on my old 10.x machines.
FreeBSD CURRENT has
zpool status [-vx] [-T d|u] [pool]... [interval [count]]
Illumos manual https://illumos.org/man/1M/zpool
zpool status [-Dvx] [-T u|d] [pool]... [interval [count]]
-D Display a histogram of deduplication statistics, showing
the allocated (physically present on disk) and referenced
(logically referenced in the pool) block counts and sizes
by reference count.
Please correct this part of manpage in all supported versions.
I've checked 13-CURRENT, 12-STABLE and 11-STABLE, all have zpool status -D documented now.