[ThePowerOfFuet]

SMS is the way to go until your operator swaps the SIM on your line without your approval.

SMS is the way to go until you need to sign in from somewhere you don't have cellular coverage.

TOTP is superior in almost every way. Failing that, sending a login link (or code) to the user's email address is more secure than SMS.

[pjmlp]

Which feature phones usually used by aging population support TOTP?

[notpushkin]

Any phone that supports J2ME should do, there's several apps:

https://github.com/kwart/totp-me

https://github.com/baumschubser/hotpants

(Couldn't find one that supports QR codes, though I don't see why that would be hard to implement)

[pjmlp]

I guess there is a business figuring out how to compile out of github into phones for non-techies, specially in the aging population.

[notpushkin]

Hopefully their relatives can remember how to install JAR/JAD apps: https://github.com/baumschubser/hotpants/releases

(Yeah, the UX could be better probably, but hey.)

[pjmlp]

Sure, because everyone has a relative that knows technical stuff, why there is a hiring problem in IT at all.

[notpushkin]

To be honest, you probably don't need to have a CS degree just to remember how you downloaded pirate Java games in early 2000s.

What's your proposed solution again?