You have also B4i ( iOS ) the code is very similar, depend if you utilize "particolary" lib or you use "standard" lib ( a lot library by B4X are compatible ). For sure change graphics. But anyway if you develop the app thinking it will run on Android and iOS platform uses as much as possible standard libraries is not difficult
Windows is another thing.
Even for Windows it could be quite easy. Use B4J (free) and probably lots of your code can be easily re-used in B4J. With B4J, you also have the benfit that your Windows-app will work on Linux and Mac. With B4X-products, you are able to develop apps/programs for most platforms using nearly the same code-base with very few adaptions.
Even for Windows it could be quite easy. Use B4J (free) and probably lots of your code can be easily re-used in B4J. With B4J, you also have the benfit that your Windows-app will work on Linux and Mac. With B4X-products, you are able to develop apps/programs for most platforms using nearly the same code-base with very few adaptions.