Exploring alternatives to Apple TV subscription through Telstra fetch box

All the ways to watch Apple TV+ and more - Apple Support

Get the Apple TV app or Apple TV+ app on your smart TV or streaming device - Apple Support

Watch on these smart TVs and third party streaming devices - Apple Support

Select brands and models smart TV can get the Apple TV app among their other smart apps.

Unsupported brands and models TV can connect an external streaming device that supports the Apple TV app. That can be an Apple TV box, Roku, Fire TV, PlayStation (4, 5), Xbox (One, One S, X, S), ‘Chromecast with Google TV’-dongle, Nvidia Shield TV box, or select cable/​satellite TV tuner boxes that support apps.

Less convenient, but still supported, is to directly connect a computer or Apple mobile device to the TV screen through HDMI.

… through a Telstra Fetch box, which is hopeless.

Can you elaborate? What do you find so bad about it?

… clunky navigation … very slow …

Try finding someone (or some store, although they will probably have less subscribed apps to show) to demo the Apple TV box to you (Stan, ABC iview, Netflix, Prime, etc.). It might impress you to that choice. You can get more out of that choice if you are already using other Apple devices (iPhone, iPad, Mac, etc.). Probably less so for Windows/​Android phone users.

Apple TV app vs. Apple TV box - Apple Community

Good luck with your choice!