For the brave and the adventurous...
Attached is the latest beta BIOS F9k for the Gigabyte Z390 M Gaming.
Biggest changes that I can see are:
1. CFG Lock can be enabled or disabled directly from BIOS. We no longer need to do it from Grub shell!!
2. The return of the ability to enable or disable Serial Port.
3. The French BIOS issue seems to be gone.
I also tested the CNVi slot. Unfortunately, the whitelist is still there and we still can't use the slot for a macOS compatible Wi-Fi/Bluetooth card.
Note that, after flashing, trying to get in to BIOS with my monitor resulted in just a black screen. I had to connect it to my TV to be able to see the BIOS screen. After I made my BIOS settings, I reconnected it to my monitor and was able to see the BIOS screen again. I think this is just some weird issue with my monitor though or maybe it was CSM...
If you decide to try this BIOS, unzip it and put it on a Fat32 formatted USB flash drive. Then use the Q-Flash function in BIOS to update the BIOS. Just to be safe, I did not update the backup BIOS to this version.
* Disclaimer: I take absolutely no responsibility if you brick your motherboard!! You use this BIOS entirely at your own risk!!