It still doesn't work for me :(
I used the --options runtime flag in Xcode 12.2 on macOS Catalina and I can't install the app on an iOS 15 device.
If I do the resign on a mac with BigSur and Xcode 13, it works.
With the flag. Before resign:
❯ codesign -dv /Users/ndr/Downloads/Payload/MyApp.app
Executable=/Users/ndr/Downloads/Payload/MyApp.app/MyApp
Identifier=com.test.rd
Format=app bundle with Mach-O thin (arm64)
CodeDirectory v=20500 size=19389 flags=0x10000(runtime) hashes=597+5 location=embedded
Signature size=4736
Signed Time=7 Jul 2021 at 10:32:12
Info.plist entries=37
TeamIdentifier=XXXXXXXXXX
Runtime Version=14.2.0
Sealed Resources version=2 rules=10 files=112
Internal requirements count=1 size=192
After resign:
❯ codesign -dv /Users/ndr/Downloads/Payload/MyApp.app
Executable=/Users/ndr/Downloads/Payload/MyApp.app/MyApp
Identifier=com.test.rd
Format=app bundle with Mach-O thin (arm64)
CodeDirectory v=20500 size=19453 flags=0x10000(runtime) hashes=597+7 location=embedded
Signature size=4736
Signed Time=7 Jul 2021 at 10:42:56
Info.plist entries=37
TeamIdentifier=XXXXXXXXXX
Runtime Version=14.2.0
Sealed Resources version=2 rules=10 files=112
Internal requirements count=1 size=192