The de-skilling of retail clerk I think predates even the GUI. I think it goes back to the laser/upc/database systems of the 1970's and 1980's.

In 1970 retail clerk is a medium-skill medium prestige job. There were lots of stories of people who started as a retail clerk and end up as CEO, and even people who aren't that ambitious could still carve out a comfortable middle class lifestyle as a retail clerk. But that's because there was a reward for experience. Before the laser/UPC/DB system rolled out, you needed at a glance to be able to know the price of an orange, or the difference between the expensive and the cheap mushroom. Because there would be a paper tag on every cheap mushroom that said "10 cents", but what if someone swapped that paper tag onto the expensive mushrooms that were supposed to cost 30 cents? You needed to know the difference, and have the real prices memorized to be able to be fast enough to keep the customers happy.

This also meant that you couldn't have a large retail store (something at the scale of the modern Walmart or Target), because you couldn't get enough clerks who could remember all the necessary prices and so inevitably you would lose money to tag switching. Department stores solved this by forcing you to buy each good separately in each department- you would pay for your housewares in the housewares section and your clothes in the clothes section, and they had another whole army of clerks in the basement managing store credit to keep it low-friction enough. But that's very high-touch, demanding a lot of workers, and those people still have the rewards of experience so they are all comfortable careers.

But then the laser/upc/database system came out. And suddenly you would get a natural language description of the item (or even a picture in the modern systems) from scanning the UPC. And you could scale the store up as much as you wanted, just needed to buy a bigger hard disk for the database, so the stores tilted more towards capital and less towards labor. And that eviscerated the career path of most retail stores, because store owners no longer believed that keeping retail clerks around benefited them.

This is machines hallowing out a job and alienating workers from their labor for the benefit of capital- exactly what Marx had described a century earlier for factory workers in Das Kapital. But for reasons of class and gender we mostly ignore retail clerks so it doesn't seem to have attracted near as much attention.