well i just tried the biosflashback method and sadly it doesn't work for me

you've flashed the older bios or a recent one?

official support page  https://rog.asus.com/uk/motherboards/rog-maximus/rog-maximus-z690-hero-model/helpdesk_bios/

I've been dealing with this problem for ages on a z690 extreme. The technical support team told me to return the motherboard, and I bought the same model again. With the stock BIOS (1304), it was working at x16, and I thought the issue was gone, but ...