If my framework contains an older deployment target (~iOS 9.0), will it be backwards compatible if I create an xcframework from it? I understand that any developer using my xcframework will need to use Xcode 11+, but what should they expect if they run on older iOS versions?
Will XCFrameworks be compatible with older iOS versions?
Yes, having an older deployment target for the actual framework contained by the XCFramework is fine. Note that our recommended best practice is to support the latest shipping OS version (currently iOS 13), plus one prior version (iOS 12). The vast majority of devices support this mix of iOS versions. The App Store support website publishes the iOS version usage so you can see what makes sense for your needs.