I've been looking for shows with like Supernatural mysteries and stuff I could use as inspiration for my Chronicles of Darkness game. Currently watching the Dresden Files.
Undead Girl Murder Farce (light novels and manga available digitally from Kodansha; anime on Crunchyroll under the title Undead Murder Farce) was really good too.
I'm binging The Magicians right now and it's full of world-ending life-destroying magical rule-breaking bullshit that might be helpful inspiration, it's not like detective mysteries but it does do a lot of "here is this complicated problem and 5 twists along the way, use your creativity to solve it"
I really appreciate shows where the history matters, like they bring back guest stars all the time because things fit together rather than it being monster/problem of the week