Like every one said, this is just a speed limit placed on your downloads, 4G = 100mbps, 5G = 250mbps. You DO NOT need a 5G enabled phone to get 5G speeds. You can get a 5G plan on a 4G device and you will get the advertised 250mbps speed (theoretical...
I recently joined PM so don’t have experience of this specific issue, but you may face the issue you are describing. I recently had my dad over and he has SIM issue getting a lock on a Canadian provider for his non Canadian SIM. Needless to say while...