iOS 9.3 is supported, but the team doesn’t have access to a device running this OS version at the moment (Apple doesn’t make downgrades easy), so we can’t reproduce this issue. The minimum supported deployment targets can be found in the JUCE readme.
I found a couple of build issues when building for iOS 9 with Xcode 10.1, but these should be fixed shortly.
In case this helps, I just now compiled the Demorunner on an iPad mini from the Paleolithic and everything seems to work just fine (iOS 9.3.5, JUCE 7.0.4, Xcode 13.2.1, macOS Big Sur).
The big problem is that it will soon be impossible to distribute for iOS 9 or 10. According to Apple “starting April 2023, all iOS and iPadOS apps submitted to the App Store must be built with Xcode 14.1”, which has iOS 11 as minimum deployment target.