After DAYS troubleshooting and logging a ticket with support, this is the solution!
Confirm this issue using Premium Deluxe and the MS Store version / Windows 11 / NVidia Geforce 1070 and multi monitors (have not tested single monitor).
MS need to hotfix this urgently.
(I’ve just updated my ticket with this info)
Thankyou!
(BTW I’m wondering if it’s something to do with multiple monitors).