Domain Mapping menu no longer available

Weirdness, multi-site has been working for a while now (created & installed a new site just a few weeks ago)

But now I cannot find the Tools > Domain Mapping in Sites to be able to set the Domain of a new site.

All my other mapped sites are up & running without concerns I just can't find the Domain Mapping menu.

Updated recently but nows says 3.4.1 available but don't want to mess with things with an update.

Have a site ready to go just can't assign the domain, very frustrating.

Anyone seen this before?