Trying to wrap my head around 2FA... Any help?

It’s not google that vouches for you, but some math. The QR code you scan when you setup 2FA sets a secret on your device. Based on that secret + time, some numbers are generated that you enter on the website to confirm that you hold the secret. If you talk about “google device stuff” NOT based on QR then yes, that’s controlled by Google… BUT there are no FLOSS apps for that, afaik. Eg. With QR: Install some app (F-Droid - Free and Open Source Android App Repository) and test on this test site: Check your 2FAS Auth app — QR code