@vaarajo By default, there is a hard connection between O365 groups and app workspaces in Power BI (Group Workspaces). They are working to remove the dependancy, but as of now, I am unaware of any way to "just" remove them from Power BI. If the user is part of that O365 group, then that group will show up in Power BI for them.
Could you please mark the proper answer as solution or share the solution if it's convenient for you? That will be a big help to the others.
Wow what a disaster. I was Yammer admin a few years back and we haven't used the network since. Now I have 40 - 50 groups suddenly showing in my PowerBI App Workspaces. I thought App Workspaces were different to O365 groups? Looks like they are 'pretty much the same'.