If you haven't already, clean the X Motor, bracket and pulley

With M2 hex, loosen the motor pulley set screws and insert the printer spacer under the pulley.

With the pulley flange facing down and pinching the pulley spacer firmly, position one set screw to align with the machined flat on the motor pulley shaft and tighten that one first. Then, tighten the second set screw.

Install the X Axis Motor / bracket onto the new 2020 frame with the pulley facing up when the linear rail is facing forward. The end stop should be facing to the right.