Whats a TV series that went completely off the rails, became absurd and lost sight of its own original premise?

I hear Riverdale was like that.

Sherlock unfortunately. S1-2 are some of the best TV I’ve ever watched. 3 was okay, and then 4 was completely off the rails, with each episode being about some zany conspiracy. Granted it can’t take all the credit, Doyle did the same.
It’s been awile but was season 4 when he basically became God? Like, I get that he’s smarter than everyone but it turned into him basically containing all human knowledge in his head. “That hair on her scarf is from a Persian blah blah breed of cat only available from X thus proving she’s the murderer” without doing any research, just God-like knowledge kicking around his head.
Yes it was far less a whodunnit and more of a psychic detective show