I hate to be like this, but no it's not(at least not on my windows 10/11 work laptop). It is not active globally, the Teams window containing the call has to be active(on my system).

And it would be a problem if it was, as ctrl shift is the default binding for show suggestions in IntelliJ and Rider.

All of the following you've already mentioned but I forgot you mentioning them in my rage at MS. Figuring out if I'm holding it wrong or not revealed another silly issue however: the push to talk button is hard coded to ctrl space, unlike other keybinds it doesn't show up in the keybinds dialog.