History, context and usual conventions matter here.
Nheko was previously documented.
https://www.whonix.org/w/index.php?title=Chat&oldid=59733#Nheko
It was documented to have a client which can be used to connect to Whonix matrix chat. Availability in packages.debian.org is also a strong argument.
We now document Quaternion as a replacement for that purpose.
We rarely document or install by default programs which aren’t available in packages.debian.org. Only if there is a strong rationale. Related:
It was previously documented + there is an up to date fork isn’t sufficient reason to document it. A stronger rationale is needed.