Here in Germany, the newer generation self checkout terminals are fine. I use them all the time. No issues. The first generation ones were terrible.

The issue with the first generation was that they were too strict with bag placement, weight sensors, etc. They were impossible to use without having to call a very grumpy shop attendant to unlock them. Sometimes multiple times. They were grumpy because all this was technically user error but when a largish percentage of users run into the same issues over and over again, it gets really annoying to deal with.

They fixed most of the glaring UX issues with the newer generation. No weight sensors. No prompts to put the item in the bag it is already in, etc. The new ones basically only need people to unlock things like alcohol purchases, but are otherwise fine. The first generation was over engineered and had way too many failure modes. They still have them in some super markets but they are getting replaced with better ones.

Anyway, it's getting harder and harder to hire staff for supermarkets. These are low wage jobs and most of these people can get better paying jobs. Self checkout creates some opportunities for shop lifting of course. But that is offset by the wage savings. They compensate with security, cameras, etc.