re-enable disabled menu “save video as” chrome ext or chrome itself “Save Video As”

I think it is possible (at least in one way)

If we are using this method to “block” the menu context of the video

<video oncontextmenu="return false;">
   <source src="https://test-videos.co.uk/vids/bigbuckbunny/mp4/h264/360/Big_Buck_Bunny_360_10s_2MB.mp4"/>
</video>

Then, all you need to do is to select video element (using dev-tools) and reverse the blocking command. For instance:

document.querySelector('body > video').oncontextmenu="return true"

Will re-enable the “right click menu” + allows you to download video using the “save video as…” option

As noted in accepted answer this is a bad practice because experienced users that already familiar with dev-tools can by-pass this easily. If you intend to protect your videos, please consider using a cloud service that specialized in that specific task.