The PC on which I currently run Windows 10 is a little more than 14 years old, and it runs Windows 10 very well. Here are some things I learned (the hard way) in those 14 years that I believe account for my PC's great performance:
1- The operating system was installed with a 'clean install' - where you erase the C drive and install a fresh copy of Windows.
2- The operating system was installed on hardware that it supported by Windows 10.
3- I only install software that is supported on Windows 10.
4- I operate the computer only according to Microsoft's instructions (whether I like them or not.)
5- I backup every day.
If there was a 'secret sauce' to success with Windows, I would gladly share it with you. But there isn't. My five-step plan has worked for me for a long time.
Also: I don't worry about Reliability Index and other confusing OS theater.