no sound since the 15.4.1 update

In such a situation, I suggest that you contact Apple support directly, using this link:--> Get Support, or, even better, make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

Same suggestion I already gave you, as per this support article:--> If your iPhone is stuck in headphone mode - Apple Support

Regards

Giulio