How to have customers select country at checkout

Site URL: https://www.stonewarebarn.com

Hi all! We’re a business based in France but we do ship worldwide, however for some countries not directly on the website (such as the US) as not all of our products are able to be sent there (too large/heavy). So we set up manual invoices for these, as we can’t set up on the website to not sell certain items to certain countries. A bit frustrating but it works well enough.

However increasingly we are getting people from the US buy on our website but not change the country at checkout. It’s automatically pre-selected as France, but if people changed it to the US they would see that they can’t proceed with their order. But they don’t, and the system allows them to proceed with their US address but with France as the country. Which is obviously incorrect and not calculating the correct shipping cost at all.

Is there a way that the customer HAS to select their country? Instead of it being default on a certain country? At least this way they might realise...