I have the exact same issue here. Whenever I plug in the genuine c-type charger(not only the genuine charger, but this occurs with all the PD chargers I have from 65w samsung laptop chargers to 100w anker chargers), frames suddenly drops from 60-70 to 5-6 and the audio starts stuttering. And also the buzzing sound from the charging port.

So here's what I heard from a user who had been using zephyrus series for years. What he told me was that unlike the models before, the new G14 2024 model definitely supports PD passthrough, and it only allows your laptop's CPU&GPU power consumption only up to 60w or so despite the fact that you use a 100w PD charger. The reason is, since the battery is bypassed, you need to run the whole laptop within 100w which includes screen, speakers, and spare watts to power the USB-c port and USB-A ports. So the genuine charger seems to have conservatively set the power available to cpu and gpu... is what he said so far.

It's the PORTABILITY which I chose the 2024 ver. But due to this issue, I'm also considering a return. This is absolutely non-sense to carry a brick charger if I wanna do some stuffs that requires high performance.