Not sure as I have no experience with workspace apps but is the connection to agol shared with the user running the app?

So workspace app is set up by the administrative_agent user. The workspace app is available through (what seems) a public link. So to check I made the AGOL connection an user-parameter. When setting up the workspace app I can see all the connections, but once I check it in the app no connections are visible. this does indicate the user accessing the workspace app are not having the same right as the administrative agent. However, how do I figure out what type of user right I set for my workspace connection so that a workspace app can see it? 

Again, I don’t know anything about workspace apps. But I do know where to set permissions on connection files. This can be done under user management, but also under manage tokens. I suspect you need the latter. Go to the profile icon on the top right of your fme server user interface and select Manage Tokens. I think you will see a workspace app token now. Click it to open. Go to Connections and make the changes needed. Then scroll to the bottom of the page and click OK to save changes.

That is my understanding as well, you need to grant the token that was created, when you made the app public, access to the connection

Thanks Nielsgerrits and hkingsbury for your reply. This was indeed the location I was looking for. Did know there was an option for that!