One thing that price theory stresses, beyond Walrasian competitive models or supply and demand is that all markets are connected through prices, but not only prices. People also adjust on quantity, as the previous example shows. Moreover, there are many margins that people can change their behavior with the changing circumstances. People aren’t chessmen you move on a board at your whim. There are innumerable subtleties that our models will always miss.
There is always another margin where people can adjust and substitute on.
Since about forever, young unskilled and poorly socialized people have worked for a while at low or no wages while they pick up skills. Historically it was understood, and part of the employer’s obligation to give them skills and training as part of the deal, to “teach them the trade.” This still happens. Hang out at any small business, and see a teenager sweeping up and learning a lot about how the world works. For rich white college kids it’s called internships. The minimum wage, restrictions on gig work, and other labor force interventions saying employers must offer either 8 hours full time work with benefits or nothing, cut off this long-standing institution for those on the lower end of the labor market.
So the main effect of minimum wages is to encourage, nay to force, employers to be more picky about who they hire. It benefits the few who are already good workers and can put up with a harder, less flexible schedule, fewer other benefits, and so forth. It hurts the others, many of whom miss the second chance, the on-ramp to legal work.
It’s not so much about how many jobs there are. It’s about who gets them.