NVIDIA has announced that all GeForce RTX 30 series graphics cards, desktop and laptop, will support Resizable BAR by the end of March. In-game performance benefits will vary, but NVIDIA claims it will be up to 10% in some cases. Independent benchmarks suggest that AMD has the lead over NVIDIA currently with its Smart Access Memory, though.
https://www.notebookcheck.net/NVIDIA-to-bring-Resizable-BAR-support-to-all-RTX-30-Founders-Edition-cards-by-late-March-AIBs-will-issue-VBIOS-updates-too-but-initial-performance-benefits-will-be-minimal.525794.0.html