What is the need of use interface in C#

Interfaces provides flexibility, we can define a single implementation that can implement multiple interfaces. when you want to inherit implementation from a base class it is a good choice to use Interface
In short it provides loose coupling, component-based programming, easier maintainability, makes your code base more scalable and makes code reuse much more accessible because implementation is separated from the interface, Interfaces add a plug and play like architecture into your applications.

Lets take example of vehicles, in that some are 4 wheeler, some are two but the common things is that each vehicles wheel are round shape, all are moving so these similar property we can keep in an interface and can inherit them for 4 wheeler and 2 wheeler also.

Don't forget that C# doesn't support multiple inheritance, so this is implemented with interfaces.

C# - Inheritance[^]

That was my one cent to the topic.