Hey Kevin i inboxed you. Thanks
Nevermind, resolved it somehow

Here are the steps below if someone needs it.
This is what worked for me at least.
1. Have the original Injustice 2 Mobile installed
2. Install Lucky Patcher
3. With the Lucky Patcher do the patching of the signature (steps below)
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1- Open Lucky Pather
2- Tap on "Toolbox" -> "Patch to android"
3- Check "Signature Verification status always true" and "Disable .apk Signature Verfication", then apply changes. After this maybe your Android device will reboot automatically. If your Android device not reboot automatically, continue to the next step.
4- Still in the "Patch to Android" menu, check the "Disable signature verification in the package manager". Apply changes, and done! (May reboot automatically)
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4. After patching with lucky patcher, uninstall the original game
5. Download the unsigned APK (non root)
6. Run it and run the game , wait for the (Downloading resources) to finish
7 Enjoy!
This worked for me !