The turbo charger is essentially a gas-turbine and it needs to be rotating at full RPM to get maximum efficiency during launch. Earlier the MGU-H (directly connected to the Turbo-charger), used to get the engine running upto the desired RPM but with the new regulations, the Turbo-charger essentially follows a gas-turbine startup sequence.
Also, when at full throttle, the car Turbo-charger would reach the required RPM quicker. Conversely, if the car is not at full throttle, the RPM of the Turbo-charger starts dropping, decreasing the Max power output of the engine
A "not yet up to speed" Turbo-charger can result in slower launches in best case or triggering anti-stall in the worst case
But this is only applicable if the Turbo-charger is completely idle.
A very plausible approach to mitigate this would be to have the drivers drop down to low gears even on the straight and use full throttle to approach the grid. This will keep the Turbo-charger spinning and charge the batteries as well.
Of course, based on where a driver is starting on the grid, they will have to time it differently #cars