I’ve seen some distros - when you install Google Chrome - create application icons in your desktop menuing system for chrome extensions (e.g. Google Docs, Calendar etc, and youtube).
I think that’s where it comes from… There’s no dedicated “app” for youtube on Linux that I’m aware of. Similar to what you see in the “nine dots” menu when using a browser and logged into e.g. Gmail :
This doesn’t seem to happen with Brave Browser on Pop!_OS - but I have seen it on Ubuntu after installing Google Chrome.