Wikipedia's information is a little ambiguous:

The booster's tanks were reported as holding 3,600 t (7,900,000 lb) of propellant, consisting of 2,800 t (6,200,000 lb) of liquid oxygen and 800 t (1,800,000 lb) of liquid methane. However, current booster prototypes can only hold 3,400 t (7,500,000 lb) of propellant.

Depending on how current "current" was when that was written, the booster carries no more than around 800 tons of methane fully loaded; 14% would be 112 tons. Add another 30% or so for Starship and we're up to 145 tons.

The total amount of methane in the atmosphere is about 5,000,000,000 tons, so this is an increase of about 0.0000029%.

Note that the FTS is designed to get combustion started, so most of the remaining methane was actually burned. Even if none of the methane burned, the destruction of another 344,000 Super Heavy boosters late in ascent would increase atmospheric methane by 1%. //

for comparison May 22, 2023 Pipeline Technology Journal: Two Fields In Turkmenistan Leak More Greenhouse Gases Than The UK: Leaks Could Be Easily Fixed estimates 2.6+1.8=4.4 million tons per year (2022) for just these two newly-discovered leaks. So the max here is 0.0002 "newly-discovered annual Turkmenistan leak units". It is true that burning it and converting it to CO2+H2O might be greener, but... –
uhoh
11 hours ago