I think that porco is more volgar than maiale. Porco is often used as an insult, like in "Sei un porco!", or as an imprecation ("Porca puttana" means "Pig whore"). Personally I think that a sentence like "Ho mangiato del porco" would be more unusual than "Ho mangiato del maiale". To put it bluntly, porco is more volgar, when you are talking to a friend you can say porco instead of maiale; maiale is more formal and it is commonly used to indicate the animal (in animal books you will always find the pig as "maiale", no as "porco").

In realtà, si usano praticamente come sinonimi. La parola "porco" è più popolare e informale

in my video on yt I explained what porco means https://youtu.be/STYw_8dkB1c