How do I set up international roaming on an iPhone 13 Pro Max with an e-SIM?

Does your plan cover roaming abroad in the country where you are/want to go? It depends on many things, it depends on your settings, on your carrier, on your plan and on the carriers that your carrier use in the foreign country, it could be a patchy signal, or a slow connection. Can you contact your carrier and ask?

You contact your current carrier and sign up for their International plan, assuming they have one.

On the iPhone it’s in Mobile Service>Mobile data options>toggle on data roaming

Do you have an international calling plan option enabled from your carrier? If yes, contact them and ask about the connection issues.