Iphone 11 Pro Max - no sound when new texts come in

Make sure do not disturb is switched off and your phone isn’t on silent, the switch at the upper left side should look like this.

You can also adjust the volume of your ringer in settings > sounds and haptics.

If it’s still not working are you sure the speakers on your iPhone are actually working? Generally at this stage there’s no reason sound shouldn’t be playing when you receive a notification.

OK, is it all apps doing this or just 1?

If it’s just 1 go to settings > notifications > (press the app in question) and make sure “sounds” is enabled for that app.