[6SixTy]

On paper any PCIe 2.0 motherboard can receive a BIOS update adding ReBAR support with 2.1, but reality is that you pretty much have to get a PCIe 3.0 motherboard to have any chance of having it or modding it in yourself.

Another issue is that not every GPU actually supports ReBAR, I'm reasonably certain the Nvidia drivers turn it off for some titles, and pretty much the only vendor that reliably wants ReBAR on at all times is Intel Arc.

I also personally wouldn't say that Sandy Bridge is very usable with a modern GPU without also specifying what kind of CPU or GPU. Or context in how it's being used.