Say you want to design a mobile app and the like a few stuff about some design choices and decisions on similar apps designed... You'd like that in your app design wouldn't that be copying
- Get familiar with the platform specific design guidelines. It will make you to know all the rules, constrains, etc. There are official guidelines for iOS, Android, Web etc. iOS: Human Interface Guidelines. Android/Web: Material Design. Web: The best one currently is Fluent Design System by Microsoft.
- Do best practice research.
- Do not open Dribbble, Behance to find inspiration if you are not familiar with the rules and constraints of the UI design.
Getting to know the basic rules of the platform is the right start for all UX designers. You will be able to design a completely fine interface. It may not very nice, but aesthetics are secondary. Later you will learn that too. Then you can do a best practice research to find the right solutions and patterns for your specific problems. Unfortunately, most of the UX/UI designers are just copying designs from Dribbble without understanding the context or just understanding that what is uploaded there, 90% of it is not feasible or even may harm the business, as these are just for showing off. So only open these websites, when you are already know how to "read" and understand everything you can find there. Do not copy the aesthetics. Copy the system, how these work instead. But for this, you have to understand them.
You don't have to reinvent the wheel per-se.
If for example, the navigation system is very easy to use and self-evident then by all means implement a similar system.
Many sites/apps follow similar formatting and layouts. There are universal concepts that make websites and apps more usable.
I would make sure you are not copying anything artistic. You can implement a similar structure, but don't copy the exact design.