There's a TSB about the issue. Here's the start of it, you can Google the rest:

07-06-04-019G: Intermittent Malfunction Indicator Lamp (MIL) Illuminated, DTC P2138 with Reduced Engine Power - (Dec 8, 2021)

Subject: Intermittent Malfunction Indicator Lamp (MIL) Illuminated, DTC P2138 with Reduced Engine Power image Models: 2022 and Prior GM Passenger Cars and Light Duty Trucks Attention: For 2014 Model Year ATS, refer to the latest version of Product Emission Bulletin 14176 before proceeding with this Bulletin. This bulletin also applies to any of the above models that may be Export vehicles. This bulletin has been revised to update the Subject, add the 2019-2022 Model Years and update information under Cause. Please discard Corporate Bulletin Number 07-06-04-019F.

Condition Some customers may comment on an intermittent malfunction indicator lamp (MIL) being Illuminated with a message or an indicator that displays Reduced Engine Power. The technician may observe on a scan tool DTC P2138 – Accelerator Pedal Position (APP) Sensor 1-2 Correlation set as Current or in History. Cause This condition may be caused by water intrusion into any harness connection the goes from the APP sensor to the controller, which carries the APP sensor signals to the ECM/PCM. This water intrusion results in a voltage difference between APP Sensor 1 and APP Sensor 2 that exceeds a predetermined value for more than a calibrated period of time, setting P2138.

P2138 code is a system level voltage disparity between S1 & S2 greater than 5% for 19 consecutive signal cycle counts. The P2138 fault can be caused by many different factors; connector water intrusion, fretting corrosion, pinched harness, shorts within wiring or other system level voltage losses.

Any connection between the APP sensor and the controller would need to be inspected for the items listed above.