How to limit the available countries?

I think your requirement doesn't belong this module. I guess you're using the address module, if so, you can following this document https://docs.drupalcommerce.org/commerce2/developer-guide/customers/addr... to limit the available countries.

Indeed, if you have an address field on a profile bundle on your site, you can configure that field to change the allowed countries.

Automatically closed - issue fixed for 2 weeks with no activity.