These steps should allow you to u se various features of your iPhone without being interrupted by notification sounds, such as when streaming audio to a Bluetooth device.
You can use Do Not Disturb to prevent notifications from interrupting while your iPhone is in use. If you go to Settings > Do Not Disturb, then scroll down t o the Silence area, then tap/select Always rather than Only while iPhone is locked, notification sounds won’t be heard at any time Do Not Disturb is active.
To activate Do Not Disturb, from the Home screen (apps showing) or Lock Screen, swipe up from the bottom of the screen and tap to highlight the circle with a Moon in it. As long as that button is highlighted, notifications won’t be heard.
Remember that to silence the phone entirely, you still have to turn off the ringer switch on the side of the phone, unless you have adjusted the Allow calls from options in Settings > Do Not Disturb. Allow Calls From can be set to Everyone if you still want to receive all phone calls.