Thanks Klojum..
I checked the link you provided and researched on creating API key for YouTube developer.
I have a smart TV (not extra smart) in living room. Everyone can watch YouTube without any serious settings and configuration. Netflix and Amazon Prime are also available and everyone enjoys. I checked, Amazon Prime and Netflix are not included by any addon and there is workaround for it. I haven't gone through it. I want to make similar system using my RPi4 which will be in bedroom. I use this RPI4 for multiple purposes, each has different SD and USB drive.
Is this the only option; creating API key for watching YouTube on Kodi ...? Limitations are always accepted but simple prerequisites makes end users happy.