Hello, I developed an theremin simulator for iOS which tracks your index finger and thumb via cam and map it to note and volume. The distance between thumb tip to index finger tip mapped to volume and index tip mapped to note. When you open your thumb volume is max. Try it out and let me know what you think. It’s available on TestFlight as a test version.

Can't upload an ipa to App Store Connect for an hour.

You can use threshold value to detect whether there is no number. If the prediction accuracy is below this threshold value you can say it as no number

I believe in Swift. Xamarin would be nice choice as a cross platform with native output. But I guess it has also a learning curve and some disadvantages. It also will ignore my Objective-C know-now. Am I too judgmental about this?

I worked full stack. Developed both server side and desktop side with C#. Consumed WCF services in iOS apps. I want to work in iOS development. But I am afraid of losing my experience for C#.