Make life easier
Usually this product is created to solve a problem. Tech companies that do this usually falls into one of 3 categories: hard-tech (AI, autonomous-driving, bio, etc.), productivity (CRM, emails, analytics, etc.) and then "messy" tech (many APIs, logistics, telcos, etc.)
Hard-tech is straight forward. People know it's technically/scientifically hard problem to solve, so engineers like to build them, investors like to back them. This is usually driven by technology-push into the market, rather than market pulling the product out to the world, as there's usually some level of threshold/breakthrough that needs to happen to create value. Once this breakthrough happens, these companies tend to lead the market for a long period of time (e.g. Tesla in EV, microprocessors in the early days, iPhone/Android, etc.)
Productivity tends to be highly competitive, as the entry barrier tends to be lower, until someone gets to a market monopoly position. Note taking apps, CRM software, HR/recruiting software, etc. falls into this category. There's usually many players that compete for same budget and it's hard to break through the noise in the market. But if you can become the source-of-truth or default workflow, you can create a lot of value for the customer.
Messy tech is interesting. Think of API companies that create abstraction layer for your software. They "do the dirty work" so that you can simply call API requests and receive the responses to get the job done and APIs abstracts away the complexity and messiness that may lurk behind the scene. A beautiful toilet is like an API. You do your thing, flush it down, then the toilet (and the sewer management system that's connected) take care of the rest. Most messy tech tends to deal with complicated implementation, compliance & regulations, aggregation of 3rd-party integrations (bank payments, telco partnerships, etc.) so they let you operate in a 'clean' world.
Make life fun & enjoyable
This product is built to bring joy to people. Content business like games, video, and music falls into this category. Also other things like recreational drugs, drinks, and casino (yes, it's not there to help you become rich, but it's built to give you fun (and take away your money) may belong in this category.
It's hard to define a 'problem' for these products. Maybe you found an inefficiency in this industry and define that as a problem, but the customer value is usually in entertainment value, which is quantified mostly through retention, session lengths, and ARPU (average revenue per user). So what you are ultimately competing for is attention and time spent on entertainment.
How to know which one to work on
This surprisingly is influenced by the founders' personalities. Some prefer one way over the other, and it's actually not as common to find founders doing both directions well. People tend to have preferences/biases that leans towards one way or the other.
Listen carefully to your inner needs and motivations. Pick them carefully as once you go down a path, as it will take you time (assume 10 years to build something decent), so you probably want to work on something that gives you a sense of purpose in a lasting way.