The later Mission Impossible movies (from 4 onward) are great popcorn cinema, but every once in a while they'll throw in a more serious death to raise the stakes. I feel like they aren't too dark, tonally, but it'll depend on your tolerance.
Strange New Worlds is a pretty fun Star Trek show, although even it has an episode or two that hews more intense. For the most part, though, it's fairly light-hearted.
Right now I've fallen down the British Mystery Hole and have found myself watching no fewer than three (3!) different BBC mystery series. My favorite of them is Ludwig, a 2024 series about a reclusive puzzle designer - crosswords, sudoku, chess puzzles, you name it. His twin brother, a police detective, goes missing, and his sister-in-law recruits him to unravel what happened. He does this by posing as his brother at the police station, and inevitably getting drawn into murder investigations, which he solves using puzzle logic rather than police techniques. It's very funny and charming, and makes for a good, cozy watch.
Not quite so cozy is Luther, a series that I had been meaning to check out for some time. I've been a big fan of Idris Elba since I saw The Wire, but this is the first thing I've seen him in since then where it seems like he really gets to stretch out and properly act. It's a much darker mystery show, with a tortured protagonist, an excellent Moriarty stand-in and a whole slew of (mostly) serial killers to catch. It also gets bonus points for having Saskia Reeves, who I adored as Catherine Standish in Slow Horses. I'm nearing the end of the first season, and the show has so few episodes that I'll probably have watched all 5 before long.
