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.
On a related note, it blows my mind into pieces when I'm standing behind people in line who clearly have no idea how to self checkout. I don't get it. Self checkout has been around for like 25 years. It's not new and it's not complicated.
I've shown my parents how to do some tech tasks many, many times. And they still don't get it.
Maybe, similar to self checkouts, it's a combination of being so used to doing things a different way or not needing to do something at all, deeply believing they are "bad at tech" and creating a self-fulfilling prophecy, and knowing it's easier to just ask for help than to actually become proficient on their own.
Around for twenty odd years and the experience hasn't noticeably improved in that time. I act like a neophyte on self checkout because I refuse to use it unless forced.