The line is if the symbols/works are used in a context so they clearly intentionally, or by unnecessary/unreasonable lack of care, create confusion. Someone who looks and sounds like McConaughey just being themselves isn't a violation.

Look at existing trademarks. They are riddled with high similarity filings, but they co-exist as long as they are not used to create confusion.

The bar for any enforcement would be very high for humans, simply looking and behaving like themselves.

But if someone very much like McConaughey was used in a commercial portraying a fictional "famous actor", that wouldn't go over. Unless ... it was clearly a parody. Or in fact, they are also an actor, and small signals indicate which actor, avoiding reasonable confusion problems. Or any other reasonable mitigations are taken.

McConaughey couldn't even sue a movie about him, with reenactments of real incidents in his life, using an actor naturally/made-up to look nearly indistinguishable, as long as it was clear the actor was not McConaughey. (Using computers to create an exact likeness might be challengeable, depending on the specifics - as they would essentially be lifting his face directly from him. Which gets into the realm of unreasonable, because it wouldn't be a reasonable requirement of any bio to go that far.)