^^^^ lobsenza got in there before me

probaly not a defective brake boooster on a new car - but possible.
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From what you guys are describing.... "If" when you first get in your car you step on the brake pedal
and release it before attempting to start the engine, you have released stored vacuum in the brake servo/brake booster. When stepping back down on the pedal it will be firm. The engine must be running so that manifold vacuum can build back up and restore normal brake function.
Additionally, when the engine doesn't start with your foot on the brake pedal it may be an indication that a microswitch, linked into the interlock system that prevents accidental starts, and is connected to the brake pedal mechanism is adjusted in a manner that requires significant pressure on the brake pedal. 'Without the vacuum assist' you may have to press down really hard to get enough pedal travel to signal the interlock, telling it that it is OK to start the engine.
On my Genesis, even if I deplete the vacuum in the brake servo, it will start with with very light pressure on the brake pedal.
You may not get much satisfaction from your service dept on this complaint. If the engine does start with firm brake pedal pressure and the brake servo is functioning, the response will be "functioning normally"
Be cognizant when first entering your car that you are
not stepping on the pedal until you are ready to start the engine and see if that helps.
I've watched my wife use the brake pedal for leverage when getting herself positioned in the seat.