It is all public information. Plus, logically, it is a low barrier to entry business with zero moat. There are lots of sellers willing to sell for barely above cost.

These are the two biggest grocery only retailers in the US:

https://www.macrotrends.net/stocks/charts/KR/kroger/profit-m...

https://www.macrotrends.net/stocks/charts/ACI/albertsons/pro...

This is the single biggest grocery retailer in the US, but not solely grocery:

https://www.macrotrends.net/stocks/charts/WMT/walmart/net-pr...

Costco obviously moves a ton of groceries.

https://www.macrotrends.net/stocks/charts/COST/costco/profit...

Target now sells a wide range of groceries in all of its stores too:

https://www.macrotrends.net/stocks/charts/TGT/target/net-pro...