"It has a flat tire."
Translation:Elle a un pneu crevé.
The Swiss french Goodyear website has: https://www.goodyear.eu/fr_ch/consumer/learn/fixing-a-flat-tire.html#
Guide réparation de pneu plat
So why is
Elle a un pneu plat
Probably to make it an adverb meaning "on/down to/to... a flat surface".
It is also used figuratively: "je suis à plat" = I am shattered/bushed.
"It" is gender neutral in English but its translation can be masculine "il" or feminine "elle". There is no real reason to default to masculine since "une voiture" and "une moto" are feminine, while "un camion" and "un véhicule" are masculine. This is why both "il" and "elle" versions are accepted.