Hello the problem is the same of: https://www.drupal.org/project/commerce/issues/3388335 🐛 Unable to disable Tax Number verification Active
It is no longer a problem with the VAT Number module but it is a problem with Drupal Commerce.
You have to make sure that when you uncheck the checkbox, the verification does not really happen, even for European tax codes. The current solution is to edit commerce/modeles/tax/scr/Plugin/Commerce/TaxNumberType/EuropeanUnionVat.php
but obviously it would be better if this is fixed in the next Drupal Commerce release.