Hello @GB
The technical limit for Windows 10 is 8TB as seen here: https://learn.microsoft.com/en-us/windows/win32/memory/memory-limits-for-windows-releases?redirectedfrom=MSDN
But, It's entirely possible that this is a limitation in your BIOS or your PCIe root complex. The BIOS does BAR assignments at boot time. Do you have a relatively high-end motherboard, or is it a cheap one? Do you know which chipset it uses? I don't know how many BIOSes can assign physical address ranges outside of the "PCIe hole" below 4GB.
Hope this helps with your query,
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