[speedwell68]

Thank you, it works.
I followed the steps to generate those 3 keys.
Started my media player, enter youtube addon settings, switched OFF "use developer keys" and switched ON "enable personal keys".
Then entered 3 keys. (man, doing that with the IR remote and onscreen keyboard, was more than 10 mins!).
Pressed Ok, and it works!
And indeed, no need to login to youtube.
THANK YOU!

I never login on Kodi either.  I just use it as a cast receiver from any of my devices.  I gave trying to enter those keys in the UI and just did it in the terminal.  

As an aside, is there a way to paste something into the Kodi UI?  

Easier if you just edit the settings file on your player from your PC via network: \Userdata\addon_data\plugin.video.youtube\api_keys.json 

I just added my credentials to the file in the Kodi install on my Linux desktop in Nano and copied the modified file to my Raspberry Pis running LibreELEC using SSH.