I was not happy with the standard Greek keyboard so I made my own version. It is not much different as you can hold Shift+CTRL s to get the third version of Stigma (ς) or press "w" in my version. And changed Upsilon to u/U and Theta to y/Y (since it is next to T).
1. extract the folder and run "setup". 2. Restart your computer 3. type "windows settings" in the windows search bar at the bottom left of the screen next to the windows icon and press enter 4. select Time & Language 5. select Language 6. You should be able to see Greek - Custom keyboard 7. If not then click add language and then select Greek - Custom. 8. From here it is easy to use these keyboards as one of your options to select in the bottom right of your screen next to time and date.