The country of the number you choose is not cosmetic. It decides whether many services will send you a code at all.
When the country matters
Services that operate per-market — local banks, delivery apps, telecom operators, government services and most national retailers — will only accept a number from the country they operate in. A foreign number is rejected before any message is sent.
When it usually doesn't
Global products generally accept a number from anywhere. For these, pick whichever number is actually receiving right now rather than worrying about the flag.
Pricing and content follow the number
Some services infer your region from your phone number and will show you different pricing, currency, language or catalogue as a result. If you want a specific region's version of a service, that is a reason to pick that country deliberately.
Choose availability over preference
A live number in a neighbouring country beats a dead number in your first choice. Each country page separates numbers that are working now from archived ones, so start from what is actually receiving and narrow from there.