Those with UKEE region, try sending your phone to the nearst Oppo service center and tell them to downgrade to an early Android 10 version, then use the switch region guide to change to Europe EUEX (dual sim). Don't bother with VPN, updates are controlled by EE.
However, not every service center can downgrade. From my personal experience, the one in my city (in central Vietnam) could not do it. When I came to Australia, I sent my device to the Oppo center in NSW and they did it successfully.
That's the only way to escape from EE bull****.