IE's monopoly was replaced by Chrome and Safari's, and Safari only exists because Apple gives you no choice but to use it on iOS. Firefox had a brief spot on top, but it really didn't last that long.
Windows still has the vast majority share of desktop.
Yes but that's my point. Monopolies don't last. We have other ones now yes. But that's because the earlier ones died.
And yes we still have windows as the major desktop OS but don't forget, in the 90s/early 2000s windows was equivalent to computing.
These days the desktop OS is much less relevant than it was and many people don't even own a laptop or desktop anymore. They just do everything on their phone. And Microsoft totally and completely lost that race.
Chrome is the outlier there. It didn't come with any desktop OS and still got near 100% market share, even before Android contributed to that. How? It's worth studying.