In Australia, tons of phones were rendered useless during the "3G switchoff". What was not mentioned about this switchoff is that lots of 4G devices were affected - specifically those that supported VoLTE but were not endorsed by the carriers. I got one of my old phones IMEI's blacklisted just by using the Pixel IMS app. It worked for about 24 hours before the phone got blocked.
From what I remember the issue was that many models of phone would use 4g/5g for everything but emergency calls, which was done over 3G. So the government made the choice to block those phones from the network entirely rather than leave them seemingly working but unable to make emergency calls.
The carriers then responded, "I notice that there is no requirement that we allow any device that can make emergency calls. So we will only allow devices we also sell (and maybe a few other models, if they're popular enough that we can't get away with not allowing them). And if that means more people than necessary will have to buy new phones, we will happily sell them new phones."