OK, so which computer platform should you choose?
IMO, the best choice for most people is Chrome OS (a version of it called Chrome OS Flex runs on old PCs, but is not as good as Chrome OS yet (at time of writing, doesn't run Linux or Android programs): hopefully it will get better over time).
However, you cannot run Windows programs on it. There are two basic options:
1. Run hosted Windows: best option for this is probably Cameyo - but you have to pay (people usually charge to run your programs on their computers)
2. Use Boxedwine. This is free and open source, and the concept is ingenious IMO.
Boxedwine is a mini version of Linux, compiled to run as Web Assembly (WASM), which means you have Linux right there in your browser! It's "emulated" Linux, not a compatibility layer, so it will run more slowly. The clever bit is that this emulated Linux has Wine installed - so now you can run (most) old Windows programs on it!
To be fair, performance is poor right now - but this is the way of the future: all programs on all platforms.
More and more professional software is being offered on multiple platforms now anyway - and there are now several good options for developers who want to develop for multiple platforms (my personal favourite is Flutter, because it produces quick, light code, whereas options like React bundle in a "mini web browser", so that your "native" app is actually a "browser" app running natively).
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