Text to Email Authentication

Say your Apple ID is example1@icloud.com signed in Mac system preferences , click on plus sign enter another mail address say example2@gmail.com .

A pop window will appear on Mac , open the gmail account the code will be received , come to the pop window in Mac and enter it .

Click on next the new mail address will be verified shown with arrow .

Again open mail application from Mac a verification will appear .

A pop up window will appear after some time on Mac .

Note : your trusted numbers are already verified to get the code , those are stable and phone numbers can't be changed to mail address however you can add new mail address and verify in the 2FA account .

See the articles Two-factor authentication for Apple ID - Apple Support

Get a verification code and sign in with two-factor authentication - Apple Support

See the article Use two-factor authentication for security on your Mac, iOS devices, and iPadOS devices - Apple Support

You have to enter the mail address that is other than your primary Apple ID that is signed in Mac system preferences , click on next .