I just had to connect to wifi for the update to start, the button was greyed out. If you don't trust me on this, I can send you a screenshot when this happens.
Wait a second, yesterday I misread your comment, is this only available on 5G and not below? What is the reasoning for gating it to newer phones and countries that have that infrastructure, considering my pixel has no issues updating over 4G?
Apple has an agreement with the carriers to not allow iOS updates over pre-5G networks. Carriers used to be able to (possibly still can?) disable things like FaceTime over cellular too.
