I have not been inside a grocery store for over a year... But I have not seen any major changes in my curbside pickup order, no major out of stocks, no major substitution.
With Walmart and HEB curbside in the Austin area it's been very common for subs/out of stocks.
Going into the HEB over the last week has shown rapidly fluctuating stocks in many items. For example diet drinks of almost any kind were sparse in the store. Meat and cheese was well stocked, but bread was half stocked. Then I may go another time and the items that are missing are in stock and something new is missing. Very hit and miss.