CNAM is the database you're looking for, maybe LIDB too. Once you port the number the CNAM should change.

The number gets classified differently in the "official" phone number database when you port it to a new carrier, including Google Voice. I used to have my US number in GV but ran into a lot of the 2FA issues as as well as trying to use it overseas extensively. Eventually, Google will figure it out to the point where it is no longer tenable to try and keep working around it. I caved and bought a $5/mo eSIM plan from Tello. They don't seem to care that I'm not in the US 10 or 11 months out of the year. I can use wifi calling to send/receive texts for 2FA for free, and iOS even supports using the data of one SIM/eSIM as the "wifi" for a different phone line also present on the device. So even if I'm out, I hop into settings, turn on the second line, it uses my EU data plan to fetch new messages via "wifi calling" and then I get my 2FA code or whatever. Takes about 30 seconds in total.

Is it the most convenient thing ever? No. I have an older iPhone because I'm a cheap bastard so I turn off the other line when I'm not using it, otherwise it will constantly look for a compatible roaming signal which it will never find because I have not authorized any international charges on that account (battery drain).