I found the "F5c_n" BIOS file here: www.gigabyte.com/Motherboard/X399-AORUS-XTREME-rev-10#support-dl-bios
This bios is listed in the Version column as "F5c", but the filename when you download it contains "F5c_n" now. It did not used to be named this way months ago when I first downloaded it. BTW, I have not installed this version yet. Based on your comment, maybe I won't.
Version F4 has been fine so far, though I have suffered from 2 issues (sorry to go off-topic here):
- I could not enable the 3200 XMP profile for my Corsair 4x16GB kit directly. In another thread I found, it was necessary to install just 2 modules, enable the 3200 XMP profile in BIOS, save and restart, shut down, install the remaining 2 modules, and reboot. This was the only way to get all 4 modules running at their rated speed of 3200 MT/s via the XMP profile. Yes, I tried setting the speed and timings manually.
- The Aquantia AQtion AQC107 10 Gbps network controller disappeared temporarily. To make it reappear I found online that I had to power off, disconnect the power supply's cable to the wall outlet, drain the PS of any stored charge, wait a few minutes , and then restart.
I hope this is helpful.