Why do you think that you can only have one of them ?
There are two functions, notification mute and rotation lock. And there are two places of controlling them, the small switch above the volume control on the right-hand side of the iPad, and Control Centre (swipe/drag up from the bottom edge of the iPad's screen). Which of those two places is controlling which function is set by Settings > General > Use Side Switch To i.e. if you have that set to 'notification mute' then the on/off switch on the side of the iPad is controlling mute, and the icon in Control Center will lock/unlock rotation (grey icon means unlocked, which icon locked) ; if you have the switch set to control 'rotation lock' then the on/off switch on the side is controlling rotation, and you will have an icon in Control Centre to mute/unmute notifications.
So if you want to hear sounds and not have rotation lock then it doesn't matter what you have Settings > General > Use Side Switch To set to, as you want both mute and rotation lock 'off' - so you need the switch on the side of the iPad 'off', and the icon in Control Centre grey