Customize YouTube to work exactly the way you want it to.
I'm using this all the time myself. There is no login to YouTube required and it supports adding subscriptions and doing everything important you can do on YouTube.
Since they are integrating a web browser in the app
are they, though? I thought they just grab whatever data Invidious API fetches and display it with their method of choice, similar to how mobile clients for Invidious and Piped work. PlasmaTube manages to do similar thing without becoming a single purpose web browser.
Since they are integrating a web browser in the app,
You can do this in a better way by using something like Photino or Tauri that uses the OS' native browser engine. There's no need to bundle a browser with every app (like Electron does).