We don't have a list of officially supported frameworks indeed, we are planning to add, but we do have customers who are testing apps developed with the Xamarin framework and with other frameworks, for example with React Native and Ionic/Cordova (Flutter is in our documentation).
For Xamarin apps we have a limitation which is that the apps cannot be instrumented, which means for example that you cannot use the UFT Mobile simulations for a Xamarin app.
If you do encounter an issue when testing a Xamarin app please submit a support ticket and we will look into it.