With a number of windows open on the Desktop, clicking any application Taskbar icon may not always minimise that window.

Nothing wrong with your system. It 'may be' a bug in Windows, and if so it is unlikely to get fixed. Another possibility would be a coding error in the application. My guess is that Microsoft expects certain features to be encoded in all Windows applications, eg File/Edit/View menus and so on, and if the "Taskbar minimise" is one of those expected options, it may not be well coded in the 3rd party application.

However, I have noticed this with Windows' own native applications so I always put this down to a "Windows thing". There are many of those, Happy