How to use FFMPEG for good/professional screen recording?
Solution 1:
You can pause the recording by clicking on the command prompt, causing 'Select' to be appended to the title of the window. When you want to unpause, switch back to command line and hit any key to bring it back to focus and resume recording.
To fix the blocky encoding I modified your command to this:
ffmpeg -f gdigrab -framerate 60 -i desktop -b:v 1000k -b:a 20k output.mkv
It still has a rather low framerate, so you might look into GPU NVENC acceleration for FFmpeg. However, the better alternative would be OBS, a software actually designed for screen recording