I’m thinking of things like the invention of the automobile, typewriters, calculators, even writing. Before those were invented people did things very differently - they walked or rode a horse, wrote manually, used slide rules or basic arithmetic algorithms like long division, memorized things and persisted them through story telling rather than persisting them in writing.

People are still actively acquiring the knowledge to do things the old fashioned way in those areas, a hundred or even thousands (for writing) of years later. But typically they only do it if they need to or find it interesting.

It’s hard for me to think of any technological advance (outside entertainment) that actually caused a mean regression in peoples’ effectiveness, or for people as a whole to completely stop acquiring the skills of doing something the old way to deleterious effects. Like, has there been any invention that was so easy to use that people got worse at the task the tool was invented for? In aggregate it may happen if the tool greatly reduces barriers (like training, experience, or study) to entry, but I kind of doubt it happens for specialists.

Note by effectiveness I mean the general task, not the specific skill that may have become obsolete. I’m not effective at all with a slide rule but I have a Python shell, the internet, and hardware capable of floating point operations.