

The CO2 emissions are calculated as an average across all newly registered vehicles of one manufacturer. The reference is 2021
So if Porsche sells one 911 Turbo S with 266g/km VW has to sell 43 ID vehicles because the fleet emissions of VW group in 2021 were 118g/km.
They need to reduce their emissions by 95% from 2021 to 2035. So from 118 to 5.9g/km.
To achieve an average emission of 5.9g/km across a fleet of registered vehicles where one emits 266g/km you need 266/5.9=45 vehicles. 44 zero-emissions vehicles and one fossil-fuel-burning track-tool.
43 was a previous rounding error on my part.