You MIGHT be able to make a Xamarin project that is cross platform. I haven’t done that and it probably isn’t as good as doing native as Marc suggests. I don’t know if Xamarin requires the Mac be present. It might still require that. I haven’t really played with Xamarin, but it is something you MIGHT want to work with.
I recently did a bunch of stuff making apps for Android using the latest Delphi Tokyo version. Kind of a mess there if you ask me. At least compared to working in just .Net/XAML.