I don’t have the option to allow critical alerts on my iPhone 12 mini

I guess my long explanation wasn’t clear.

If there is no option to turn it on, it is required that it be on by law. It is thus already on so you don’t need a switch to turn it on.

In some countries it is not possible to disable critical alerts. I don’t know if that is true in the UK (it is in Canada), but if it is then there will be no switch as it can’t be turned off.

What do you mean by critical alerts? And where (what country) are you located?