Customize the Alert Slider
The sound and alert slider on the left top side of the OnePlus 5T is one of the company's signature features. It's similar to the iPhone slider, only far better.
OnePlus gives you three different slider positions for sound profiles. However, to expand on that each one is somewhat customizable. This way you can instantly silence your entire phone, silence everything but alarms, or silence everyone but a specific contact. All of this just works and happens without turning the screen on. Simply change the alert slider and you're all done.
Go to Settings > Alert Slider > and adjust each option to your liking. By default you have Ring, Do Not Disturb, and Silent, but each one is pretty customizable, and I wish every phone had one.