Guest account not created with External User and verification code

One of my users wants to set an alert for an external user. To receive the alert the external user must be listed as a guest user in our Office 365 portal and therefore they need to login the first time.

But the problem is, that the user only receives a verification code, he doesn't get the option to create or login with a Microsoft account.

Now I tested it with a new Gmail account, I indeed receive a verification code an not an option to create an account. After user the verification code the guest user isn't created in our tenant.

So I created a Microsoft account with the new Gmail account, invited the test user again thinking I know would get the option to login with my newly created Microsoft account, but nope, a verification code again.

So what is the proper workflow here?