I suspect you are looking at Gross Vehicle Weight- which is the maximum weight of the car plus its maximum payload (fuel, other fluids, passengers, cargo).
Depending on how your 2020 GT350 is optioned I suggest that your car weighs ~3,750# as it does not come close to the 4,600# that you indicated earlier.
After taking delivery of my 2020 R I decided to weigh it on the way home and it came in at 3,705# with ~3/4 tank of fuel and this car does not have the 12 speaker/subwoofer in the trunk option.
Lastly, I hope that the previous owner of your GT350 finally came to his senses and offered to provide you with the original GT350 owners kit!