Moving to a different state / province / country with ADHD

Currently, I live in Alberta, Canada. And I am planning to move to Ontario, Canada later this year. And then some time in the future (maybe 2 years from now), I want to move to a different country (either the UK or the UAE). How does one get their prescriptions when they move locations? For example, will I need to wait like 4 months again for an appointment + diagnosis from another doctor if I move to Ontario? I’m sure that’s relatively easy. But if I move to the UK or UAE, how the hell will I get diagnosed again in those countries? What is the ADHD treatment like in UK or UAE? I know that some countries make it completely impossible to get diagnosed. In fact, in my home country, you can’t even get ADHD medication even if you get officially diagnosed. Am I eternally stuck in my current location because of my diagnosis?