I understand that you were attempting to make that point and I am countering it. Do I need to be clearer?
For the cash register there are professionals that design, build, market, sell, ship, install, etc. of course.
What happens when the self checkout replaces it? The professionals then design, build, market, ship, install the self-checkouts. Same amount of jobs.... LESS the clerks that manned the registers. Where do high-schoolers, the disabled, and frail old people whose SS doesn’t pay the bills go to work instead?
See it does NOT replace the jobs at the same rate when a new product replaces an old in the case of automation. The same roles exist for the piece of equipment, but the role of operating it (which employs far more than those behind it) is gone.
The same thing happens for automation of assembly lines. The same number of roles exist for the people designing, building, and implementing the equipment that assembles things. There are no more than there already were in those processes because the roles are essentially the same. And there are far fewer roles at the operator level because there is no need for them. Where it took an assembly line of 50 there are now machines and a technician or two, not 50 technicians. Those assembly linesman don’t just become designers or marketers of new products.