I just ran across this article: https://www.theatlantic.com/magazine/archive/2020/11/why-british-police-shows-are-better/616479/?utm_source=pocket-newtab
Seems relevant to the topic at hand! I'm sure many here would agree with the author.
I've really only got Netflix so Marcella, Happy Valley and Broadchurch are my top 3 but are all extremely dark. I watched Marcella and then closed my curtains and slept with the light on.
There are so many: light and enjoyable but the best are deeper and darker; Foyle's War, Silent Witness, Shetland, Morse triad, Spooks, Sherlock Holmes and Poirot etc. The thing about British dramas is that they give you time to absorb the impact of a situation rather than a quick cut to the next scene, unlike the US productions.