Nutritional Integrity of Cooked Meat

I know a lot of us are considering cooking our pets’ food until we find out more info about H5N1 (bird flu) virus.

Over the years I’ve seen people here and there say that cooking homemade meat affects the nutritional integrity of the food and that you can’t just add a completer like you would with raw. I’ve seen others say it’s fine.

What is the consensus surrounding this? Could I cook the meat, refrigerate/freeze the leftovers, and add the completer to the meat AFTER cooking, like at time of serving?

This is specifically about cats’ diets, if that makes a difference.