Some PCs with Thunderbolt connections won’t receive the Windows 10 October 2020 Update or Windows 10 May 2020 Update until Microsoft and Intel work together to fix an issue. The companies recently discovered a driver compatibility issue that affects PCs when connecting to an external NVMe SSD through a Thunderbolt connection. To stop PCs from being affected by the issue, Microsoft has placed a compatibility hold that prevents PCs from upgrading to Windows 10 version 2004 or version 20H2.
Microsoft explains the cause fully on a support page (emphasis added):
Intel and Microsoft have found incompatibility issues when Windows 10, version 2004 or Windows 10, version 20H2 are used a Thunderbolt NVMe Solid State Disk (SSD). On affected devices, when plugging in a Thunderbolt NVMe SSD you might receive a stop error with a blue screen and “DRIVER_VERIFIER_DMA_VIOLATION (e6) An illegal DMA operation was attempted by a driver being verified.” Affected Windows 10 devices will have at least one Thunderbolt port.
Microsoft clarifies that it placed the compatibility hold to safeguard potentially affected PCs. The company also warns that people should not try to manually update their PCs with the Update now button or Media Creation tool if their PC has been blocked from an update.
Microsoft and Intel are working on a resolution for the issue, which should come in a future update.