I started using grocery self-checkouts during COVID, but I've kept using them because there's rarely a line (and I'm a misanthrope). I'd probably go back to using regular human checkouts if I had to dig through all my crap to prove what I bought.
Having said that, I've noticed myself making mistakes. I've accidentally failed to scan an item, and I've accidentally entered incorrect codes for produce. When I notice, I fix them, but I've probably missed a few.
I guess the easiest answer is for grocery chains to reinvest some of those windfall profits and hire more cashiers.
What I do is deliberately go to a cashier, even if the line is extremely long, and I see more and more people doing the same. This forces more lines to open. One time they asked if I could use the self-checkout to speed up the process. I replied that if the items were cheaper at the self-checkout, sure, otherwise I'd stay in line.
I noticed this at my local Loblaws. At first they only had one to two lines open and they were extremely long. Now they have several lines open and it's very fluid.
I do the same thing. Aside from a gas pump, I no longer will use self-checkout for any reason. I'm done working for Big Retail for no pay & no discount.