2015 Buick Verano not starting

My mom’s 2015 Buick verano has been giving me issues with diagnosing why the vehicle won’t start. I replaced the battery and starter/solenoid thinking those could be the issue. Still nothing. Vehicles lights turn on and warnings saying “service stabilitrac”, “fuel level low”(I checked), “service traction control”.

There’s no sound other than a single click from what sounds like the starter when you push the start button.

Starter has power and the fuses aren’t blown.

Only code being thrown is U0100 “Lost communication with ECM/PCM A

Any help would be greatly appreciated thank you!!!