Ultra Resolution in Diablo Immortal is available on the PC version, and the following devices:

iPad Pro 2
iPad Pro 10.5
iPad 2019
iPad Pro 2018 11
iPad Pro 2018 12.9
iPad Pro 2020 11
iPad Pro 2020 12.9
iPad Air 2019
iPad 2020
iPad 2021
iPad Air 2020
iPad Pro (11-inch) (3rd generation)
iPad Pro (12.9-inch) (5th generation)
iPad Air 5th Gen (WiFi)
iPad Air 5th Gen (WiFi+Cellular)