If you see Resizable BAR supported in HWInfo but it only shows 256mb and smaller sizes you could try overriding the Resizable BAR supported sizes
To my knowledge GTX 16 series have it with smaller sizes only not sure about RTX 2000. ReBarUEFI is open source you can edit the source code to add a supported sizes override like what is done for the Sapphire 5600 XT Pulse (code is taken from Linux and it had the override for that GPU) ReBarUEFI/ReBar.c at master · xCuri0/ReBarUEFI · GitHub. You can read the PCIe 3.0 spec to see where the bits have to be set in the supported sizes for each size.
Do I recommend doing this ? No it probably won’t work and you shouldn’t try unless you REALLY know what you’re doing