I don't know how in the world the US government gets their inflation numbers, but our grocery bills have gone up about 35% since pre-pandemic period. No changes in menu, number of people eating, or any such thing. This is all anecdotal -- it is a reflection of MY experience and it doesn't necessarily apply to anyone else (but it probably does).
It does seem that the increases have been erratic and different between items. Russet potatoes went from $0.99/pound to $1.29/pound and have recently come back down (hurrah) to $1.19/pound. The cost of most oils went up quite a bit. I don't restock cooking oils that often so my memory is more likely to be fuzzy but I believe they went up more than 50% and possibly as much as 75%. One might say -- who cares about oil -- but I think that the increase in the cost of cooking oils has influenced processed food prices quite a lot as processing foods often requires cooking oil.
On to processed foods, including the ultraprocessed ("junk") foods. We try to keep those limited but they certainly are still a part of our diet. In one way, the increased prices of those is "good" as it gives incentive to not eat them or, at least, reduce the amount they are in our diets. One famous brand of stackable potato chips went from $1.69 pre-pandemic to $2.65 post-pandemic (a 57% increase). A carton of 12 cans of soda went from $5.25 to $9.25 (a 75% increase). One of my sons, who goes grocery shopping with me, is currently attempting to wean himself off of canned sodas -- in part due to the prices.
I do not have the background knowledge on the reasons for the various price increases. I can read media articles but I haven't read anything that goes back to source material. So, I can only go according to the reports of "supply chain" failures and lack of people for various manual needs in food production. Certainly, a small amount of it has been due to reducing the underpayment of various people doing those manual needs in order to entice them to come back to work (before it was safe to do such, in some cases). But the source of the majority of the increases is a mystery to me. But, let's say they were real and caused the "laws" of supply and demand to move those prices up.
Besides that ten cents per pound decrease in the price of potatoes, I cannot think of many items that have gone back down. Can you? Whatever causes there were to increase prices are likely gone, correct? There is at least one case in Europe right now that is confronting a food producer to give justifications for their continued price increase. At least the prices seem to have stopped their rampant growth though I noticed, yesterday, an additional ten cents per pound for ground beef (about a 2% increase -- insignificant though still raising questions).
One method that grocery stores and food producers use to avoid reductions in prices is SALES. Rotate the sale prices among the various items. Some sale prices are as much as 60% off. A local grocery store often has a 'buy two, get two "free"' sale on cartons of soda. Lately, it has been 'buy two, get three "free"'. Snack chips have 40% sales and 'buy one, get one "free"'. These heavy discounts do two major things. They give the illusion that prices have gone back down (without officially causing "deflation") and they keep the demand moving which would normally decrease with the increases of prices.
Another thing that food producers can do to influence perception is to change amounts per item or general size. Prices I have a reasonable chance of remembering and comparing (recognizing that memory is one of the most precarious things). But, do you remember how many ounces of potato chips were in that bag three years ago? I sure don't. I am pretty sure the sizes of the sack containers have decreased but that does not necessarily mean the amount inside of the sacks has reduced.
In our economic, and political, situation in the US there isn't much that can be done about increased prices. We live with them and hope that prices aren't raised again for several years -- when general inflation has moved up enough to justify current prices. In the meantime, bulk purchases and sales discounts and bundling are our best bets to stretch the food budget.
