Warum kann ich kein google AR core benutzen?

Günter Katze  your ZTE is not a device that is deemed compatible . Here are the ones that are:

• Asus Zenfone AR
• Asus Zenfone ARES
• Google Nexus 5X
• Google Nexus 6P
• Google Pixel, Pixel XL
• Google Pixel 2, Pixel 2 XL
• Google Pixel 3, Pixel 3 XL
• Nokia 6 (2018)
• Nokia 6.1 Plus
• Nokia 7 Plus
• Nokia 8
• Nokia 7.1
• Nokia 8 Sirocco
• Honor 8X
• Honor View 10 Lite
• Honor 10
• Honor V20
• Nova 3, Nova 3i
• Huawei Mate 20 Lite
• Huawei Mate 20 Pro
• Huawei Mate 20 X
• Nova 4
• Huawei y9 (2019)
• Huawei P20, P20 Pro
• Huawei Mate RS Porsche Design
• LG G6
• LG G7 One
• LG G7 ThinQ
• LG V30, V30+, V30+ JOJO
• LG V35 ThinQ
• LG Q6
• LG V40
• LG Q8
• Moto G5S Plus
• Moto G6
• Moto Z2 Force
• Moto Z3
• Moto Z3 Play
• Moto Z2 Force
• Moto X4
• Moto One
• Moto One Power
• OnePlus 3T
• OnePlus 5
• OnePlus 6
• OnePlus 6T
• Samsung Galaxy A5 (2017)
• Samsung Galaxy A7 (2017)
• Samsung Galaxy A8, Samsung Galaxy A8+ (2018)
• Samsung Galaxy Note 8
• Samsung Galaxy S7, Galaxy S7 Edge
• Samsung Galaxy S8, Galaxy S8+
• Samsung Galaxy S9, Galaxy S9+
• Galaxy Tab S3
• Galaxy Tab S4
• Xiaomi Mi Mix 2S
• Xiaomi Mi 8
• Xiaomi Mi 8 SE
• Mi Mix 3
• Pocofone F1
• Vivo Nex S
• Vivo Nex dual display
• Sony Xperia XZ Premium
• Xperia XZ1, Xperia XZ1 Compact
• Xperia XZ2, Xperia XZ2 Compact, Xperia XZ2 Premium
• Xperia XZ3

Also, these devices will need to have at least Android 8.0 in order for ARCore to work.