Can we freaking sell them dumbphones, then, and stop destroying portable computers for everyone else with that excuse?
Which incidentally is often just a pretense for other motives?
If computers have suddenly become so dangerous for normal people, and they want smartphones nonetheless, add to them a dumb-mode encouraged at the initial setup, and requiring some third party assistance to turn it off once enabled..! (and forbid apps to change their behavior if it's not enabled)
"Can we freaking sell them dumbphones"
Nothing is stopping the guy at Walmart or Tmobile from selling them dumbphones, or are you implying they are forced to?
Lots of dumb phones are trojaned on a firmware level. Trojans are different, but in general they allow the third-party (malware author) to accept SMS and forward them over internet. This is used to register accounts on a services which requires a phone number.
Here's my article about that from 2021. It's for the devices sold in Russia, but this issue is worldwide: https://habr.com/ru/articles/575626/
And here's more detailed research of two particular devices: https://notes.valdikss.org.ru/trojan-digma/