I'm going to cheat on this one. The worst episode is the entire final season, where everything is being clearly filmed post-COVID, there are lots of scenes where it's clear that they're limited to two actors in a room, and where it's also post-George Floyd so you have them trying very awkwardly to reconcile the fact that they're a cop show in 2021. The show ends up having no idea what to do with itself and suffers for it, eventually settling on "true change has to come from within the system," which is just taking every lesson a lot of people had to learn from the protests and throwing them out the window.