It took me ages to find this link, I don't want to lose it.
https://forums.developer.nvidia.com/t/enabling-resizable-bar-on-rtx-30-series-gpus-in-linux/239950
There will be notes.
Maybe.
There are absolutely no notes.
After dickin' about for ages to get the firmware flash tool and everything ... I just had to enable the setting in my BIOS.
yup.
Check yo' BIOS first, folks.