Window control in color tab is grayed out; not selectab

I tried to follow the instruction in the following 2 videos,that detail how to redact a car's license plate number in a video, using the 'blur' method:

I had some success, but unfortunately the edges of the drawn polygon had less blue intensity than the central part of the screen.

After messing around with Gaussian blur, I went and deleted the node entirely.

When I go to 'window control', to draw a new polygon, nothing is selectable.
https://i.imgur.com/ymmWTtD.png

You need a node to put it in.