I disable bluetooth on my phone, though periodically I find that it's back on.

Edit: iOS

I used to fervently keep my bluetooth off on iOS, and I learned that if you turn it off via the Control Center, then it automatically gets turned back on the next day. But if you turn it off via Settings, then it only gets turned back on when the system software updates. (I stopped doing this a couple iOS versions ago, though, so it may have changed since then.)

I have the opposite experience: GrapheneOS has an option to automatically turn your bluetooth off after a configurable period of not being used. So when I need to use bluetooth, I turn it on like normal. Then, without thinking about it, it automatically turns off. The end result is my bluetooth is only ever on for a couple hours each month when I'm making phone calls.

I miss wired headphones for this purpose. It's the only reason I even have BT enabled.

With iOS the easiest way to make sure it off and stays off is to build a shortcut to cut off wifi/bluetooth. Otherwise it's typically off until you get geolocated as being back home/work and wifi comes back on.

I have a "store mode" button that just kills wifi/bt that I hit before I go into any store.

Android now has an option to enable it every day.. (I have it disabled).