It is not recommended to cook chicken breast on or after the use-by date and then store it in the fridge to eat later. The use-by date is provided by food manufacturers as a guideline for the maximum date by which the product should be consumed to ensure its safety and quality.
Once the use-by date has passed, the safety of the chicken breast cannot be guaranteed, as harmful bacteria may have multiplied to unsafe levels. Cooking the chicken after the use-by date does not necessarily make it safe to eat because some bacteria produce toxins that are heat-resistant and can still cause food poisoning even if the chicken is cooked.
To ensure food safety, it's best to adhere to the use-by date and avoid consuming chicken or any other perishable food item that has passed its expiration date. If you have leftover chicken breast, it's advisable to refrigerate or freeze it promptly after cooking and consume it within the recommended storage time for cooked chicken (usually within 3 to 4 days in the refrigerator or up to 3-4 months in the freezer). Always follow proper food storage guidelines to reduce the risk of foodborne illnesses. When in doubt, it's safer to discard the chicken rather than risking potential foodborne illnesses.