Perhaps it’s Luther, Line of Duty, Broadchurch, Endeavor, The Tunnel?

Or Midsummer Murder, Case Histories, Professor T?

It doesn’t sound like Death in Paradise, Brokenwood Mysteries, The Frankenstein Chronicles, Annika or The Fall.

BritBox has a list of tv series similar to Sherlock, Alienist, etc.

There’s Haden Clark but that’s gruesome. There’s a TV series about it on AppleTV and somewhere else I can’t remember but same title.

I’ll come back if I think of anything else. Good luck!