I don't know about developing on MAOS, but, if you ware willing to develop on Windows, then you can develop a single app and run it on Windows, macOS, iOS, and Android. A 3rd party library, FMX Linux, enables the building of FireMonkey applications on Linux.
You have two choices of programming languages: C++, or object oriented Pascal, which is simpler.
The great thing is that you can drag and drop GUI components, such as buttons, list boxes, check boxes, memos, meus, etc, etc, etc, almost like a paint program, then add code to handle user interactions with them.
It's not cheap, at just over $1k. But, the community edition is free, making it ideal for hobbyists. In addition to GUI components, there are also internet & database components, etc, plus thousands of 3rd party components, many of them free.
Check out the full feature list here.
I forget he exact figure, but if you earn more than ?? %5k ??? then you are expected to buy a $1k license, so not a major hardship. I have been using it since Santa gave me Delphi v1 back in '95, and don't use anything else for developing Windows apps. It is rock solid, with tons of resources, forums, discussion groups, etc. Super quick to develop apps, and excellent debugging capabilities.
That said, if you prefer open source, check out Lazarus IDE, which is reasonably compatible with the OO Pascal version of Embarcadero's RAD Studio and can build apps for 15 platforms.
Eye candy follows:
Just drag these onto your app's form, and add code to handle them.