Try turning off “Dynamic Crowds” in settings. I didn’t notice much difference in how the crowds behaved, but it supposedly simplifies their AI and pathfinding to cut down on CPU use. It helped me a lot in the city.

You can actually have the game ask for opportunity attacks. If you open your character tab (or party view), up at the top, there’s a tab for “Reactions”. You can set it to automatically take opportunity attacks or ask before.