Microsoft’s original source code

My understanding of Microsoft's success was it came from marketplace maneuvers, many ranging from unethical to illegal, not from quality or innovative hacking. Compare Windows with any contemporaneous MacOS, for example. They took over the office productivity software market by illegally leveraging their Windows monopoly. Their initial and core success - getting DOS on IBM PCs, which led to the Windows monopoly - was simply leaping at a business opportunity, I think even before they began developing the product.

Didn't they generate fake errors for Windows running on DR-DOS, or something like that, even though it ran fine? Do you mind that they tried to destroy and monopolize the open web (thank you Mozilla!)?

So it's 1992, and OS/2 still isn't happening.

But you can get a 386 at 16 or 25 MHz complete with maybe a 40 MB hard drive, color monitor, 256-color VGA, a couple megabytes of memory, and licenses for MS-DOS and Windows 3.1 for $1000 or less. This will let you do a lot of computer things.

If you want to run Mac OS, the very cheapest Macintosh you can get is the Mac Classic, and it costs $1695 for a 7 MHz 68000, a single floppy drive, no hard drive, and a 1-bit black and white display. This will enable you to do a lot fewer computer things, much more slowly.

Macs were very expensive. Windows was good enough. It wasn't better, necessarily, but it wasn't strong-armed onto the market by shady maneuvers either -- at the time of Windows 3 and 95 it was genuinely good "product-market fit". Microsoft, from its earliest days, was good at leveraging mass-market hardware to deliver "good enough" software that worked for the majority of people. Of course they did shady stuff that increased their dominance, but Windows would have sold like hotcakes either way.

Didn't they generate fake errors for Windows running on DR-DOS, or something like that, even though it ran fine?

IIRC that code existed, but was commented out in the final build.