Obviously I’m strukc blind as I fail to find the invite button, which should be on my user page as well as below each thread.
Would anyone be so kind as to point me in the right direction.
Screenshots welcome 
Perhaps You will try this wich you find under each post:
Hi Soko,
thanks for taking the time to answer.
Sorry it took me so long to reply. I was sure it wasn’t about sharing stuff but wanted to dig up proof first before coming back 
I forgot, where I stumbled across the inivtation stuff initially but I can show indirectly that invitation must be meant to be dedicated functions other than sharing:
If you check the available badges users can collect on the forum, there is one for “sharing your first post” and another one for “when you invite someone to join the community via the invite button on your user page, or at the bottom of a topic.”
Must be two different things then, I’d say
Coming to think of it: is it by chance a function that has not been enabled by the forum administration? Or even a bug? Or is it still me struck with blindness? 
I think I found the answer myself: I checked the source code of this site to find out what forum software is running (Discourse), which then led me to this thread/post: https://meta.discourse.org/t/invite-friends-functionality/6078/2
Default setting seems to be that trust level 3 is required, before you can see the invite tab
1 Like
Hello,
didn’t recognise the badges before… 
As you can read [here] (https://help.nextcloud.com/badges/2/member), with trustlevel 2 (Member) " You can now send invitations from your user page or individual topics, create group personal messages, and have a few more likes per day."
The thread can be marked as solved…
Ciao,
Joachim