Iirc Apple switched all users to 2FA
That doesn't explain why it is when I start looking at generating an app specific password for apple mail, the first thing that pops up is a message telling me I need to enable 2FA, which is when I stop the process.
Plus this is only affecting a couple of older PPC systems, none of my relatively newer Intel macs are giving me any problems. Also I still log into my iCloud account with a simple email address and password, same as I have for several years now.
If I understood the letter Apple sent out in June correctly, they said 2FA would be enabled for those using 3rd party applications (not Apple) to access their icloud data.