Hi André,
it is a distributed switch. When I try to add the host to a distributed switch by using the "Actions" menu, the only option I have is in the screenshot.

But when I right-click the distributed switch on the left, on the same highlighted switch, I can 'Add a host'. However I am experiencing a new issue of "datastore conflicts with an existing datastore in the datacenter with the same URL but backed by a different physical storage".
I tried some searching on fixing that but so far no luck in solving that issue.