My daughter was in class the other day and pinned her teacher. She then tried to raise her hand and received a "this feature is not available right now" notice. Does "raise hand" not work when the presenter is pinned?
Before you ask, yes I was having a meeting with myself :).
I can confirm that it should work as the below screen shot is using the Desktop client with pin and raise hand enabled.
The second is the same thing but in the web version.
So I think based on the message you received it is probably just something that is yet to be fully implemented across all tenants. I also wonder if it could be an education thing but not so easy for me to test that theory.