Hello!
I've confirmed that the problem is present on other systems except mine.
Any 2023 driver causes low FPS in Apex Legends (and other nonDX12 games) with 6000 series cards (tested 6600 and 6700XT) when Rebar is enabled on X79 systems with Rebar support patched into BIOS (yes, I know they are not officially supported).
Earlier drives work flawlessly (e.g. 2022.11.2).
It appears that some change in driver thrashes performance on our systems with Rebar ON, so just to inform you.
Thanks!