I don’t know about Google’s “free” numbers, but third-party VOIP numbers are usually blocked for 2FA verification. I’ve tried that. Most places won’t accept it, because they know you’re trying to get around the tracking. The 2FA isn’t the point, and the cost of the phone isn’t the point, the tracking is the point, and Google’s “free” numbers are absolutely tracking you just as effectively as any telecom is.