It kind of depends on if he does it ironically or enthusiastically. It’s not that concerning if it’s like the satanic temple that’s more a political activism, as opposed to a cult with animal sacrifices. If he’s not hurting anyone or anything, then you’re probably fine, and just need to roll with it.

Does he actually worship Satan or are you one of those idiots who decides that someone worships Satan cause they wear black and got tattoos?

Were his people responsible for getting Roe v Wade overturned? Maybe his isn't the religion to be worried about.

True satanists are some of the nicest, well rounded people you'll meet. They treat others as they expect to be treated, believe in human rights and equality for all and holding corrupt governments and churches accountable, and don't judge people based on trivial things like black clothes and tattoos.

He doesn't care. Only God can judge him. ...Wait...

Is he being kind to others, treating everyone with respect, and being a good person? If so, what's to worry about? Everyone has their own path to follow--if your son is being a good person, who cares if he's goth?

Have you asked him what his religion means or are you worried for nothing?