What's funny, because what I found strange is when Mikael says this:
The creation of the group itself happens against the /edu/groups which I’ve never seen before, but that’s not interesting.
Because that's the bit I found totally interesting. Why does the PowerShell need the /edu/ endpoint?
Hop over to Graph Explorer we can play with this:
Comparing different endpoint: v1.0
It becomes clear why we need the /edu/ endpoint. It has this bit of information:
"creationOptions": [ "SkypeSpaces", "ExchangeProvisioningFlags:481" ],
The hint that a Team is provisioned seems to be the flag "SkypeSpaces"
Naturally, one would ask. So if I want to enable Yammer, Planner or PowerBI on an existing Unified Group. Do I POST an update to creationOptions?