I can't find the option anywhere, or did I miss something?
First, you can only enable it with the preview drivers, it's not in 23.9.2 or 23.9.3. Below is the link, if you can't find it.
https://drivers.amd.com/drivers/amd-software-adrenalin-edition-23.30.01.02-win10-win11-insider-previ...
Second, you can find AFMF in the driver settings under Gaming\Graphics.
Third, AFMF only works with HDR disabled.
