Make browsing the internet possible only on Chrome, Safari or Edge (with no modifications or extensions). No competition allowed in browsers.
Make browsing the internet possible only on macOS, Windows, Android or iOS (no custom Android distributions, definitely no LineageOS or GrapheneOS or whatever). No competition allowed in Operating Systems, especially no open source operating systems.
Make crawling the internet possible only to Google. No private crawling and no competing search engines.
Let me know if I've missed anything...
Buying stuff is on a spectrum and I think a consumer should be able to chose a tightly regulated system for exchanging currency.
Most everything else should be free to choose.
Financial transactions could become so streamlined that a "commerce fob" is likely to emerge. That would be a credit card with a screen and buttons.
Think about how streamlined all these tasks have become. Putting those in a single ROM that has a screen and is tied into some legitimate network will emerge.
It is only out of convenience that these services are currently tied to a "phone".