How to use Look At Node in AnimBP without rolling the bone

There isn’t one.

Animation blueprint arent supposed to have any code.

The character needs to process whatever, however, and then that information in the form of whatever (here a vector) is passed onto the ABP.

Anything at all that involves any coding or parsing should never be a part of an animation blueprint.
So, the look at node is an immidiate nono.

Even if all you are doing is copying info from one bone to another - which a copy node will do just the same, and without any processing behind it - you are still in the this is trash territory.

Depending on what goal you are trying to achieve, adding in a leg IK or a CCKD or a Fabrik node with the final direction/relevant info - probably including a rotation - passed into it, will likely work a lot better. And also follow best paractice…