MS-DOS cornered the desktop market around 1981. It remained the dominant desktop OS, despite being an utter piece of crap OS and technologically obsolete even at the moment it was introduced, until around 1990, when it was overtaken by products from the same company, Windows 3.1 and later Windows 95.
Windows 95 then took over in... 1995 :-) Windows is still the dominant desktop platform in 2021, and it will probably be for at least 1 more decade.
Linux took over server environments around 2005, I think, and its still dominating in 2021. It will probably dominate for many decades more.
Smartphone OSes are in the same place. Smartphones have matured, they're primarily slabs of glass/metal/plastic. You either get Android or you switch both hardware AND software and get iOS.
Android is almost free for manufacturers and customers, so it's even worse than Windows. How is it ever going to be displaced? Keep in mind that not even beauties such as Windows Me, Windows Vista, Windows 8 and Windows 8.1 made much of a negative dent in the Windows marketshare.
