@zoomcool7 Yes this is a deliberate decision by Gigabyte to stop you from downgrading to previous BIOS due to “major vulnerabilities concerns”.
The F12 update for the Z390 AORUS PRO says:
Introduce capsule BIOS support starting this version.
Customers will NOT be able to reverse to previous BIOS version due to major vulnerabilities concerns.
I have posted a guide on how to get around this limitation here.
Please read the entire guide carefully as you can overwrite/erase your Intel ethernet MAC address!