Writing a cross-platform application (linux/windows) + statistics server. What to choose?

Question

Programming

What can be used to develop a cross-platform application as quickly as possible, or if it doesn’t work out at all, then to make porting as simple as possible? win and linux platforms.
Applications will connect to the server, collect statistics and questions, store them in their database and then exchange the accumulated information if they successfully connect to the Internet.

Answer 1

JAVA not?

Answer 2

C++, for Qt interface

Answer 3

I answered your second question, here also - the requirements are vague, but they show that any language is also suitable.
For two questions, I can assume that you are a non-IT teacher and, apparently, you have little or no experience in programming, but there is a desire to make a program for testing students.
I can suggest getting acquainted with nodejs. you can also write desktop programs on it (NWjs, electron atom) - cross-platform and server part (which is also economical in terms of resources and does not load). in the future, mobile applications (react native) are also possible
pluses - one language everywhere (desktop / server / frontend / mobile), although everywhere there will be their own nuances of course. Plus, a huge community.
also, many here will probably recommend Python, you can also write a desktop and a server, but the entry threshold will be higher.