I want to add that there is QSPI memory on the module itself, and that this contains the equivalent of a BIOS plus boot content for SD card models. That content, as used in JetPack 5/L4T R35.x, is incompatible with JetPack 6/L4T R36.x DP. This is why (so far as I know) there is no upgrade path for that without flash.