How do I made my iPhone Bluetooth hidden or undiscoverable while I am using Bluetooth?

You can’t hide Bluetooth and still use it; if it’s hidden, how does a Bluetooth device connect to it? But it is ONLY discoverable when you open Bluetooth in Settings/Bluetooth.

My answer is copied from this Apple Recommended answer:

https://discussions.apple.com/thread/253931241?answerId=257376422022#257376422022

Bluetooth is a common standard, and it is only possible to "hide" Bluetooth by disabling it.

You can turn off Bluetooth here:

Settings -> Bluetooth