Dialed phone numbers are in the wrong format (international, should be US)

The format shouldn't matter that much. It's mostly to make things easier for people looking at the number. The format is generally determined by the region your phone is set to. Go to Settings>General>Language and Region and, regardless of what it says, re-select the region. Sometimes it gets a bit confused. Also, try going to Settings>Phone>Dial Assist and if it's on, turn it off. If it's off, turn it on.

Insert a physical sim with a number from the ‘correct’/home country. (I borrowed my sons) activate that sim.

Then activate your eSIM. Finally remove physical sim.

Sorry I have no more to offer. I've traveled outside of North America on a number of occasions and never had this problem.

I've been mostly happy with iPhones, but it's little issues like this that have irked me over the years.

Trust me, Android phones also have little irksome issues.

Andauk wrote:

Insert a physical sim with a number from the ‘correct’/home country. (I borrowed my sons) activate that sim.

Then activate your eSIM. Finally remove physical sim.

Um, why would I want to do that? Not to mention, my iPhone doesn't have a physical SIM slot.

I've contacted Apple Support and after checking several places in Settings (region, phone and iMessage whether overseas number footprint existed), they told me to reset all settings.

Resetting all settings fixed it for me.

It Worked! Thanks very much!