I'm pretty sure they're just straight up synonyms. I've gotten a slightly more formal feel from "car", but you can essentially use whichever one you feel like at that particular moment.

which ever suits the sentence, sometime 'car' might be too short for your sentence so say parce que. other words...preferance

From a French post on WordRef Forum:

Parce que is much more common, car is slightly more formal.
They have the same meaning, but not the same construction:
"parce que" introduces a dependent clause, while
"car" introduces an independent clause.

There's no difference, words have the same meaning. But we're using more "car" generally speaking

https://www.duolingo.com/comment/9106899/Car-vs-Parce-que