That is why they are typically called a tutorial, and not a demonstration or sample project. Tutorial is only intended to showcase the concept and to explain the concept, it is very less likely that someone would be interested in developing an entire project, with every OOP concept just to write an article — OOP is way more broader than you might think.
Which is why, if you want to learn OOP, I would recommend taking a class at your local institute for software development and learn how to build a software with OOP concepts. There are some only websites that share the same insights as well, but the expertise level of the authors is quite questionable.
Finally, even if you did some good tutorial, chances are you are only going to see a "real world example", which is again not a full project.
Lastly, why put a condition around Windows Forms? OOP is not used in Windows Forms only, there are other frameworks and languages that can teach you OOP even better. Is this a homework? If so, then your chances to get help are even less. :D
Real world examples for OOPS concepts[
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