iMac is old 10.10 yosmite iOS - how to turn-off two-factor authentication - old iOS no provision for two-factor

See the information in the "Can I turn off two-factor authentication after I’ve turned it on?" and "What if I use two-factor authentication on a device running older software?" sections of Two-factor authentication for Apple ID - Apple Support

1: After two weeks’ enabled or if enabled when the Apple ID was created, two-factor authentication cannot be disabled.

2: Yosemite can be used with two-factor. If your Apple ID password is ABCDEF and the two-factor code received is 123456, enter your Apple ID password as ABCDEF123456

3:Any Mac running Yosemite can be upgraded to El Capitan, which gets you out of this whole case.

4: You can receive two-factor codes on Android, other phones, or landlines.

Details for all recent macOS versions, including for El Capitan: How to download macOS - Apple Support

Have a complete and current backup created prior to the upgrade, on the off chance that a problem arises.