How do I learn about productionizing a hardware product

PIs, Arduinos, and esp32 dev boards are great for prototyping, but rarely used in a product sold outright, for a number of reasons. You might use one of them for proof of concept, but, if you intend on making a hardware product, youll want to design your own pcb, etc. For example, you might use an arduino board for development, but you dont need or use 90% of the components and features the protoboards contain.

Outside of the design itself, you need to think about a lot of other stuff. Enclosure, certifications, etc. You cannot generally push a piece of hardware out without FCC, UL, and other certifications. These are expensive, and consume your product (UL will for example in some tests, set your product on fire). Youll need some sort of enclosure for your device, and youll need to research some standards for your devices placement, like if its going in a computer rack, has to have specific dimensions. If its going on a desk, be mindful of consumed space.

Electronic components are best bought in bulk, and your early prototypes will be way more expensive than your final product, depending on the quantity you sell.

Also, though at the end of all of this, market research, how many people will even find your product useful, and how many of those will even buy one, let alone more than one. Youll want to know if its big corporations, or small homes that will use it, as youll need to change design factors based on that (ex enterprise customers may expect more robustness than a residential user)