Please read the UK case again. UK is requesting apple to give them access to any user's data worldwide not only UK users or data within UK jurisdiction. Sorry to be the one to say that but China is better here.
As I said in another comment. Yes that will be the case as now EU and other countries will require Apple to not do this. There is no way Apple will comply with UK without risking being banned from most of the world. But this does not change the fact that this is literally what UK is demanding.
Incorrect.
GDPR does allow foreign government, as long as they have similar protection as GDPR, process the data for law enforcement and criminal investigation.
I'm not talking about GDPR specifically but about the future development if Apple accepts that. EU will consider it a problem when UK and later another countries request the same from Apple eventually.