Step 1: Define innovation in entrepreneurship.
Innovation means introducing something new - a product, service, process, or business model - that creates fresh value for customers or society. It is a defining characteristic that separates an entrepreneur from a mere trader or imitator.
Step 2: Evaluate "Selling old products".
If the product already exists and nothing new is added, there is no innovation. This is simple trade, not entrepreneurship driven by creativity.
Step 3: Evaluate "Copying another brand".
Copying is the direct opposite of innovation. An entrepreneur who merely duplicates an existing brand adds no new value and takes no creative risk.
Step 4: Evaluate "Ignoring customer feedback".
Ignoring feedback is poor management practice and often leads to product failure. It has nothing to do with innovation.
Step 5: Evaluate "Creating a new app for online learning".
This introduces an entirely new digital solution to meet an existing educational need in a new way. It is original, technology-driven, and value-creating - a textbook example of entrepreneurial innovation.
Step 6: Confirm the answer.
Only creating a new app for online learning meets the definition of innovation by an entrepreneur.
\[ \boxed{ \text{(C) Creating new app for online learning} } \]