I'm looking around, but I still have not found anything on the subject. I need to hide the login button when a guest makes purchases, the store is created with Joomla and Virtuemart latest versions.
If the login button is a module, then assign that module to all pages except the checkout page.
If that doesn't work, then you will need to override the login module, and then have a condition in the overridden file to not display the button for guests who are on the checkout page. Here's an answer for checking if a user is a guest.