The food industry has pretty much invented the whole process of making "addictive" products and then "test[ing] out recipes on the public to make it even more addictive". Of course, we usually call it making products that taste good, and running taste panels with the public for product development (making a new tasty thing), quality control (ensuring the tasty thing stays tasty), and market research (discovering even tastier things to make in the future). Each part of it employs all kinds of specialists (and yes, those too - nutrition psychology is a thing).

The process is the same. The difference between "optimized for taste" and "addictive" isn't exactly clear-cut, at least not until someone starts adding heroin to the product (and of the two, it's not the software industry that's been routinely accused of it just for being too good at this job).

Not defending social media here in any way. Cause and effect is known these days, and in digital everything is faster and more pronounced. And ironically, I don't even agree with GP either! I think that individuals have much less agency than GP would like it, and at the same time, that social media is not some uniquely evil and uniquely strong way to abuse people, but closer to new superstimulus we're only starting to develop social immunity to.