I can only choose 11.0 target in Build Options which leaves me with arm64 only. So - no more updates for older devices? Or how can i enable that again?
You would still build for iOS 11, but in your iOS Build -> Advanced -> Support Architectures you need to include another architectures. A common choice is armv7 + arm64.
Also, in your Deployment Target (in the info.plist) you can choose the lowest iOS version you want to support.
Xamarin Inc., as a wholly-owned Microsoft subsidiary acting as a separate legal entity, adheres to the Microsoft Privacy Statement: Privacy & cookies