Having done all three roles either formally or informally (after 15 years development) the key thing a product manager has to do is follow Steve Blanks advice and get out of the building. OK not in times of COVID but there has to be someone who actually talks to customers or potential customers in person and builds _qualitative_ opinions / insight into what really needs to be built and where the real opportunities ar…
Ideally, you don't just talk to them. You watch them work. Observe, and gather clues about what will serve their needs. And when people tell you what they think they want, don't assume that's the product spec; treat that also as an opportunity to listen to clues that will help you understand their needs.
The best products are designed around how people work, not necessarily what people say about how they work.