Does anyone know how to flash the latest asus z690 motherboards without using flashback, something like /GAN? @HHo2016 the link you sent for latest amidewin with /GAN does not work.
GAN option hasn't been available for years. If you want to try flashing a modded rom you may have some luck with fpt, but you will loose any OA3 key, serial number, uuid, and perhaps your mac id for intel lan. I think amidewin will let you create uuid (/SU AUTO??) and re-enter your serial number (System Serial) (/SS?). For lan there should be some tools posted...
You could also try flashrom to flash your BIOS (though in my experience it does not work on laptops due to custom vendor BIOS chip protection). You can compile it for Linux or for DOS (search "flashrom DOS port"). Flashrom worked to flash a Gigabyte X570 AORUS ELITE WIFI motherboard BIOS.
I personally have had it work on a MSI Z390-A PRO motherboard. Haven't tried on newer Intel motherboards.