How many such devices can still support modern TLS certificates anyway? By this logic, shouldn't we also use plain HTTP instead of TLS?
If you're using a decade old phone to sign up for a utility, you've got bigger problems in your life and no self-respecting person should be adding to them.
React already existed in 2016, so did Vue and Typescript. Never mind good old JS.
I frankly can't imagine a device capable of supporting modern TLS stacks but incapable of supporting JS. Much less a phone, which in many countries basically requires LTE (and sometimes even VO LTE) support to function at all, due to the 2G and 3G shutdowns.
- Old browsers without the modern JS features you're trying to use
- Different browsers, with different features
- JS didn't load due to network errors
Better would be to use plain HTTP in addition to TLS, rather than instead of TLS. TLS does have benefits, but if it is optional then it can also be used on computers without TLS (as well as potentially other situations where you do not want TLS or where it is not useful).