I think that windows is still the biggest but is changing very quickly to linux, for normal office work and a home computer that is used mostly for surfing and doing spreadsheets and documents, you can even use a raspberry pi running Debian without a problem. And Pi4 is much cheaper. (You can even use Ubuntu on Pi4).
I personally have to use windows 10, as my development tools are all currently only for windows. I had to move to Windows 10 as I had to upgrade my hardware and all new hardware only comes with windows 10 drivers (Windows 10 is the worst windows since windows ME).
the market shares of the operating systems do not always evolve in the same direction
the system of operation has benefited over several decades of great commercial support
At that time the traders spread across all the continents
And for those who hesitated to invest in the windows system, the salespeople offered them a real advantageous financial modality to innonder the market
windows sometimes loses market share when recent versions are difficult but very quickly by reactions of the enterprise windows the recertifications are enough to regain their share of the usual market
The learning curve on Linux is steeper than Windows. You can download Ubuntu and learn the basics by reading the user manual that is published for every version. Then there's the server manual and the administration manual. By the time you read though that you pretty much know how to use Linux. At least the basics.
Most office software is available via the software center which is basically Ubuntu's app store. Other things can be installed through Ubuntu's package manager APT. When you get into building some of the software it can be frustrating. Libraries change over time and the software you are trying to build and install may not run on your machine without Google searching for error message and figuring out which packages need to be installed and sometimes some lines of code that need edited in order to make said software work. Generally software that is worth using comes with an install script or will at least give you a working set of step by step instructions.
People who still use Windows:
PC gamers. There is little support for Gaming on Linux.
Companies who use legacy software that only runs on Windows.
People to lazy to learn Linux
People who are required to use Windows for school or a job.
People who don't care about security