Actually mTLS has been a native feature of browsers for more than a few decades now, still is. A card reader is very common in both laptops and PC's in countri

Actually mTLS has been a native feature of browsers for more than a few decades now, still is. A card reader is very common in both laptops and PC's in countries where smartcards are common. Kinda supply-demand thing. Not to mention the readers are cheap. For mobile devices you can basically use a smartcard SIM that provides similar functionality. But there are other options for secure secret storage on mobile devices. Most of the hindrance is behind the willingness to pick a solution and commit to it. Doing it half-assed and never reaching the tipping point will doom every solution.