Each site is different, but a site that works with Google Authenticator (or similar apps like Authy) will have an option to scan the QR code when setting up 2FA. You then open Google Authenticator ...

Google Authenticator lets you establish 2FA by using your phone to scan a QR code generated by the app on a separate device or by entering a key code. It’s a relatively easy process. Except ...

To use Microsoft Authenticator with a non-Microsoft site or app, you'll need to have the QR code handy from the site or app in question so that you can scan it within the Authenticator app.

and then scan the resulting QR code with Google Authenticator on another device. We like that the app verified our identity before allowing the transfer. If you enable Google Authenticator’s ...

“Here’s how it should work and how every other authenticator app out there — Google, Okta, etc. — work. When you scan a QR code for MFA, it generates a string with a series of value ...