https://wccftech.com/nvidia-rtx-a6000-ampere-gpu-resizable-bar-support-stock-vbios/

The NVIDIA RTX 3060 is the first gaming desktop graphics card to support resizable BAR and many laptops featuring the NVIDIA RTX 30 Laptop GPUs also support resizable BAR. Even AMD's Radeon RX 6000 series supports this technology. It would only be right if NVIDIA's professional-level cards support resizable BAR and with recent discoveries, the RTX A6000 supports resizable BAR. Redditor 'millenia3d' has discovered this feature.

In short Resizable BAR removes the tight restriction on the amount of data that can flow between the CPU and the GPU Memory and can sometimes allow for substantial performance increases. Resizable BAR grew in popularity and recognition when AMD implemented Smart Access Memory when you paired a Ryzen 5000 Series CPU and a 500 Series Chipset with an RX 6000 Series GPU. The biggest differentiator here between AMDs implementation and NVIDIA's is that the NVIDIA support for ReBAR (Resizable BAR) is that it's supported on many more platforms.