Looks like you don’t have it purchased through iTunes, as there is the Disney+ badge right above the Play button. If you have it purchased, it wouldn’t say to open in Disney+. Try scrolling down on that page to see the purchase options
The iTunes Extras includes the alternative ending along with other deleted/extended scenes
I prefer to buy directly from Apple Refurbished store. I’ve bought two in the past, never had any issues, practically brand new