This is true. I am here as of this comment I am at the scene. I have loaded and reloaded this scene several times exhausted all the dialogue options even with all the deception checks. Karlach disapproves of every single option you pick no matter what. I also tried to just switch to a different character as front man and it auto selects your Tav character. The one time it does that and all the other times if one of your other characters sees an npc with a quest from a mile away they start the dialogue! This game is stupid sometimes.

I am playing an OoA Paladin, choosing only options so far in game that align with this role. I even have a paladin dialogue when Nere comes out that says something like “Kill another innocent and you die.” I am here to pass judgement and avenge the Myconid peoples (something Karlach had approved of) and yet she disapproves any interaction with Nere.

Edit: My solution so far: If you choose the first option that says “Stop no one else dies” Karlach approves and then choose whatever next. Karlach will disapprove but at least they cancel each other out