I would like to control my phone via PC. I tried TW Quick Support and Host, but I was only able to point (with blue pointer) not click and trigger an action.
I have a TW account that I used in Host application.
Does the device need to be rooted?
Although some Android devices are capable of true remote control, i.e. where you can control your phone from your computer, Nexus 5X isn't one of them. From your computer you can only view the Nexus 5X screen, as you self noted, but unfortunately you can't use TeamViewer to control the Nexus 5X device.
I have found a app called Vysor that has done the job.
AirDroid can also be used to remote control a device (the functionality is called AirMirror, which is a little confusing).
For rooted devices, this works out of the box (just install AirDroid on the device, authorize root and control it from your browser). For non-rooted devices, a desktop USB connection is required, and a desktop app or Chrome extension (more details).