It will depend if Disney releases a compatible app. At present they do not appear to have plans to support IPTV set top boxes.
Disney+ Supported platforms:
Desktop Web Browsers (via streaming)
Disney+ desktop browser system requirements
Mobile Devices and Tablets (via free downloaded app)
Android phone and tablet
Apple iPhone and iPad
Smart TVs (pre-installed or via free downloaded app)
LG WebOS Smart TVs
Samsung Tizen Smart TVs
Android TV Devices
Set-top Boxes and Game Consoles (via free downloaded app)
Apple TV (4th Generation and later)
Sony PlayStation 4
Other Streaming Devices (via free downloaded app)
If you go to the main menu and go down to apps you can open the google play store and download it there! I came here to figure out how and then saw this and was disappointed but then went and played around and figured it out.
Disney+ is available on the Pik TV box specifically. It won't be out on Optik.