In series 8 (which has an identical ruleset to the current series 11), Dragapult was mainly used in a supportive role for proccing Coalossal with Surf, carrying moves like Will-o-Wisp and screens in favor of offensive options. Since series 11 started this month, it seems that Coalossal has really fallen out of favor, causing Dragapult to take a more offensive role, but it's still rare (ranked #57 as of writing this), and it's possible it may revert to a more supportive role once the meta settles down a bit. Have you actually been losing to Dragapult or do you just see it as a problem theoretically? While it's always good to cover your bases when you see a potential threat, make sure that you don't sacrifice answers to more common threats such as Zacian, Kyogre, Urshifu, or Calyrex.
Good ways of dealing with Dragapult are priority (especially Sucker Punch), speed control like Tailwind or Trick Room (although TR certainly isn't as splashable on any team like Tailwind usually is), and bulky Dark or Fairy types (although you'll probably have more success with bulky dark types overall). Zacian and Calyrex-Shadow both outspeed and threaten Dragapult with an OHKO, although Calyrex will be in trouble if it's sashed. For a non-restricted option, Urshifu-Dark has one of the most powerful Sucker Punches in the format, although it is weak to Max Airstream if anyone uses Dragapult to Dynamax (which does not appear to be the case, according to its most common moves). Incineroar is one of the best Pokemon in VGC in general and can take any of Dragapult's attacks and hit back with Darkest Lariat or Throat Chop, although Dragapult's Clear Body does make it immune to Intimidate.
