The two best flours to can used on keto are coconut flour and almond flour
Coconut Flour is very absorbent and generally you want to substitute ¼-⅓ cup coconut flour for 1 cup traditional flour.
Almond Flour may require more moisture added to the recipe. Generally the ratio for substitution is 1:1. You may need to experiment with the amount until you reach the desired consistency.
Ground flax is another good option but some people may be sensitive to flax so be sure to assess your tolerance.