The way Kroger does it is easiest for me - nearly all produce has a sticker on it; every apple, every onion, etc. Get what you want and put it in a bag.
When you get to the self-checkout, scan the barcode on the sticker, and it’ll either ask how many you have, or it’ll ask you to weigh it. Do that and it charges you appropriately.
Meijer’s version is horrible, enough to keep me from shopping there. You manually enter the code at a scale in the produce section, enter the number of items or weigh them, then it spits out a sticker you then scan at checkout…so scanning twice for the same thing. Nope!