This app was initially a clone of the other Android application that was made using Xamarin. The code for that application was not available at the time. Despite the source code being available for that part of the project now, there is a separate package that the application uses that was never open sourced so the application cannot be compiled by anyone else.https://www.dreamcast-talk.com/forum/vi ... =3&t=10128
Some extra features have been added to this version and rendering performance is much better. From what I have seen, I am not convinced that Xamarin is very useful for developing Android applications; also, there seems to be no Linux support so I would not use it for development. As an aside, I like C# as a programming language but I dislike .NET the more I program for it; I am the current maintainer of the program DS4Windows.
AFAIK, Qt has no support for making an Android widget so that would have to be done as a separate project if that would get developed.