Watch Apple TV on Mid-2010 iMac

The Apple TV+ subscription only covers Apple Original content and that is what the website makes available.

For any other content in the iTunes Store, like movies and Tv shows not produced by Apple you can access them through the iTunes Store section, in the iTunes application.

Those 2 things make up all the content you would otherwise see together in the Tv App on Catalina, iOS devices or Apple TV.

Depends on what exactly you mean by "watch Apple Tv".

You can use iTunes for purchases and rentals form the iTunes Store.

If you mean the Apple Tv+ subscription service, then you can use the website: Apple TV+

No.