Resizable BAR defines how much of your graphics cards VRAM is to be mapped for access by the CPU. Typically the CPU can access up to 256 MB of mapped VRAM, but with the resizable BAR it can have full access to the graphics cards' VRAM buffer.
https://www.techspot.com/news/88620-intel-bring-resizable-bar-11th-gen-rocket-lake.html?utm_source=dlvr.it&utm_medium=blogger
https://www.techspot.com/news/88620-intel-bring-resizable-bar-11th-gen-rocket-lake.html?utm_source=dlvr.it&utm_medium=blogger