But” is not a conjunctive adverb; it’s a coordinating conjunction. This means it can join two independent clauses in one sentence when preceded by a comma. For example, “I wanted to buy a new car, but I didn’t have any money.”
Conjunctive adverbs, such as “however,” can’t join two independent clauses in this way. They need to be preceded by a period or a semicolon and followed by a comma: “I wanted to buy a new car; however, I didn’t have any money.