How to start video record from PC? is there a way to record a video just like if I would record with a normal camera app but with the difference, that I can observe the image on the PC? I've tried IP webcam and droidcam, but both created videos with very bad quality compared to normal camera recording, I guess due to streaming limits.
But streaming is not my aim, I just would like to have a preview and then simply start recording locally to the phone.
scrcpy is a free/open source project which allows you to mirror the Android device and control it from the Windows/MacOS/Linux. It does require the device to be Android 5.0+, and have adb developer debugging enabled.

Once running I was able to with a Pixel 2 and a MacBook Air:


See the Pixel 2 screen on the MacBook Air screen
Scroll on the Pixel 2
Click on the camera app
Switch to video recording in the camera app
Click record
Click stop recording 


without touching the phone.

You would still need to get the video off the phone but the video quality is of the native camera app.