And yet Clerks does feature a few very fictional brands… because the characters discuss them and say some less than nice things about them. Nails, Chewly’s, Mooby’s, etc.

You won’t get in trouble for acknowledging the existence of McDonald’s.

But having a character talk about how they think the McRib is made of cat meat will most definitely get you sued.

There’s more to it than that of course, but as long as the filmmaker doesn’t seem to be actin in bad faith, wrongfully trying to confuse or mislead customers, or downright defaming the brand, it’s legal.

That said, it’s usually a lawsuit that establishes whether it’s legal or not, so to save money on legal fees and court costs, logos are frequently just flat out avoided when possible. Not for legal reasons, but to avoid the hassle of legal reasons.