How to stop iPhone 13 Pro ringer - audio volume from going to to 100% by itself

Latest iOS on both. When we connect to car by either cord or Bluetooth and when phone is placed on car dash charging pad, on it’s own, the volume automatically increases to 100%. Any call then received is at full volume | ringer….. And, if one receives a call you have to always manually turn the ringer lower. Also, if no calls are received, you have to always remember to lower the volume manually when leaving car or you get full volume rings….

How can we stop the ringer from going to 100% on its own, short of not using the charging pad or connecting to car?

2024 Porsche Cayenne. Porsche says it’s an Apple problem and Apple tech says it’s a Porsche problem.

Does not happen on any other car we tested it on - other Porsches also.