That's not what I was implying, but if you say that I have no idea what it means, that's not true. I just know that any program could potentially be open-source or not, whether it's the language itself, or the programs written using it.

Been a while, not sure how you are getting on with your requirement. One thing I was looking at recently is pascal, an old language which is still going. The compiler is free pascal:
https://www.freepascal.org/

And if you want a full IDE there is Lazarus:
https://www.lazarus-ide.org/

The reason I mention it is because it can compile native to multiple architectures, Win, Linux, MacOS. It needs nothing else either, no CLR or virtual machine. It may be an option, I admit I haven’t used it since Delphi days, but my issues with MVVM is pushing me elsewhere, so might look into it further.

why use it?

At this point it's completely unrealistic.

First of all I'm not aware of any tech that would allow you to compile a Mac app on Windows (nope for Java, nope for Electron, nope for Python).

Second, in practice it's impossible to expect a mac app to behave 100% same as on windows. Maybe if it's a mature app, that had hundreds of releases and already stabilized on Mac and dealt with OS specific problems, you could get away with limited QA for Mac releases, but to expect to make "blind" releases without seeing the app run on a mac (skipping the simple fact, that without a mac you can't compile a native app).

The ONLY tech that would fit your requirements is a web app, because it runs in the browser not on the OS level, so the browser manufacturers are taking the responsibility for cross-platform compatibility.

the island?

I think that's near the border of the Eurasian and the Australian plates.
Not truly cross platform.

Enlighten us please!

That's beacause you lack the neccecary technical knowledge on this topic. You can try to simplyfi thinghs to "it's just a bunch of bits", but it won't make it true. You can say that both Mac (ARM/M1) and PC (x86) are just a bunch of transistors so why can't they run the same code "it's just a bunch of bits", but it doesn't change the fact, that they can't (without additional specialized software)

exactly , it is clearly on the eurasian plate

why not just make a web app like every company does?

That's irrelevant. An executable file consists of bytes composed of bits. Any program in any OS can write a file consisting of any data it wants, ergo, a compiler that runs in Windows or MacOS could write the exact same file which could be made to execute on whichever OS it's supposed to run on, and it should still run even if it was created using a different OS.

And what I ended up doing is using Linux for it.

EDIT: Orkhepaj, this program needed far too much security to trust it to a web app, or anything Internet related. But it's long finished now, anyway.

Sorry, I seem to have opened a tin of worms. I simply necro’d this thread to point out FreePascal and Lazarus which can compile to multiple architectures, including Linux and Mac.
https://wiki.lazarus.freepascal.org/Deploying_Your_Application
Unfortunately MacOS, and apple products in general are the most closed systems, you may need to install cross compilers, or compile on a Mac virtual machine. It’s not simply an exe from what I understand. Frankly I haven’t used a Mac in decades, and I never intend to go near them ever again

Well, since unspeakable acts of thread necromancy were performed on this thread, I suppose I'll ask: What are you coding that would require such privacy as to be closed source, and yet is coded in Java?

I'll have to respectfully say none of your business, because as you said, it's private. But the only reason why I wanted to use Java is for cross-platform compatibility, which has nothing to do with the nature of the program itself or its security.

Sure it does. The choice of programming language entirely does factor to the matter of the program or it's security. Depending on how low level you'd wish to go.