Garmin's proprietary DataCard Reader uses the same USB Drivers as the older "non-MSM" (Garmin-mode) devices. Drivers are also required on the PC for modern devices to be seen in preboot mode and for older software like Updater.exe to function, because it and other legacy softwares such as G7ToWin only see devices in Garmin or preboot mode.

Contrary to that info in the old open-boats-project.org thread you linked, the drivers work fine for Win 7 and 10 in all 32 and 64 bit versions and in the 64 bit-only Win 11 for Garmin/preboot mode devices and older softwares, so it'd be surprising if the DataCard readers don't get recognised in Device Manager. You're certainly correct in musing that the DataCards weren't designed originally for Mass Storage Mode use and therefore not browsable like a removable drive in Explorer nor seen in Disk Management.

The only difference from earlier 32bit versions like XP and Vista is maybe in the placement of the driver file. For example, in Win 11 the file "grmn1200.inf" is stored in C:\Program Files (x86)\Garmin\USB_Drivers\Amd64. Perhaps there were some problems using earlier MapSource versions in 64 bit OSs when working with old BlueCharts. Probably overcome in later MS versions.