Imac 24 inch 2008 and apple tv

The Apple TV app on Mac requires macOS Catalina 10.15.

macOS Catalina 10.15 is compatible with iMacs Late 2012 or newer.

Macs with older versions macOS can still get Apple TV+ content in a browser, when subscribed. Point Safari at tv.apple.com, and sign in at the top-right corner.

It won’t be easy, as everything is discouraging you from doing so.

Pages, Numbers, Keynote:

https://apple.stackexchange.com/questions/376919/old-version-macos-sierra-for-pages-keynote-and-numbers-iwork

Office (Word, Outlook):

Microsoft doesn’t sell non-current versions, but if you have a serial number (product key) then you can download older software versions still. Some retailers may have old Office software in stock, and that might be a way to obtain a product key.

Apple TV hardware is aimed at monitors and TVs not iMac.

Apple TV app should be part of Mac OS my Mac mini from 2014 has apple TV app.

My Mac runs 10.15.5 so you're way behind.