The Walking Dead: I probably enjoyed through to the end of season 6, but was definitely getting a feeling of repetition. My wife carried on watching but even she must have gotten sick of it having not watched any of the final season.
Vikings: Good for four seasons, then went totally downhill. Never finished it.
Fear the Walking Dead: Maybe managed a couple of seasons and gave up. Too similar to the main series and with no characters to care about at all.
House of Cards: Watched one episode of the final season and gave up. Despite his real life issues, Kevin Spacey's character was the show and it suffered as a result of him being written out.
Homeland: First two seasons were great, but after that my interest wained and I gave up either through season 3 or by the end of it.
Bosch: Even from the first season I thought it was a bit slow, but I think we managed to watch three complete seasons before giving up.
The Black List: Another one were it became a rinse and repeat show after a couple of seasons, so I stopped watching.
American God's: Watched the first season and thought it was decent, but after one episode of season 2 I gave up.
The Witcher: Maybe struggled through 3-4 episodes and gave up. No investment from the books and so it just didn't capture me one way or another.
The Mandalorian: Tried twice to get into this, maybe watched 4-5 episodes. Just found it slow and boring.
Probably got a dozen shows I started to watch for a few episodes, sometimes as many as four or five, if the reviews were good, and they didn't grab me at all.
You, Peaky Blinders, Mr Robot, Mad Men, Narcos, Money Heist, The Queens Gambit, Power, Snowpiercer, Lost in Space, Line of Duty, Preacher.
There's probably more that I can't think of at the moment.