As a mod and instance admin, it varies depending on the variety of the troll and whether they're under my jurisdiction:

• Garden Variety Trolls: I just don't engage and ban them. These are the types posting racist memes, name calling, harassment, etc. I waste no time on them. Outside my jurisdiction, I report them.
• Mis/Disinformation Accounts: I usually fact check them. Not to change their minds, but to tear down the false narrative they're trying to construct. Depending on the how they're operating, I may or may not report / mod them; depends if they're violating any rules. There are some I've wanted to ban/mod but they weren't violating any rules, so my hands were tied.
• Obnoxious Jerks: Usually just don't engage at all. Sometimes the best thing you can say is nothing. If they're under my jurisdiction and are violating rules (most communities have some kind of "be civil" rule), I'll mod the offending content, ban if it's a persistent pattern of behavior. If not, I'll report them.

Otherwise, I just downvote, block, and/or move on. Life too's short to care what some internet troll has to say.