that haven't been true since pixel 4. it just picks your phone in the background.
a burner sim, like a literal criminal, is the only way today.
Its possible to set up a phone with a google account without even a sim card in it and use it as a wifi only device, so Im pretty sure what your saying is wrong.
assuming the number you get hasn't previously been assigned to a google account
It still works without a SIM card, how do you explain that?
Even with a burner sim, there is the International Mobile Equipment Identity (IMEI) number, which is tied to the phone, and is known to all apps with the android.permission.READ_PRIVILEGED_PHONE_STATE permission.