Here is an excellent article explaining when and how the GF can be watched.
Foxtel/Kayo replay available at 11:15
Game can be streamed from 7plus app but only on certain devices (why I have no idea)
You can stream the Grand Final live on the 7plus App, but only on selected TV’s or set-top-boxes. Importantly, you cannot watch the game through the 7 App on your mobile phone or tablet, as is the case for all AFL matches and the Brownlow Medal, which caught many people out on Sunday night (see below for info on how you can watch it on your mobile). This is due to broadcast restrictions put in place by the AFL. You can watch the game through the app on the following devices: Telstra TV, Samsung Tizen (2016 and later), Fetch TV, Apple TV, PlayStation 4 & 5, Android TV, Google TV, LG TV. You cannot use Chromecast or AirPlay to watch the Grand Final and you cannot watch a replay of the game on the app.
you can watch it on a mobile through the AFL app
Some good news late Friday night by the AFL, with confirmation the AFL Grand Final will now be able to be streamed live on your mobile device through the AFL Live Official App