Another tip: FAQ V0.1 of Using Win32Image Manager v1.0 to flash buster release 2020feb05 image on a 16GB SD Card - tlfong01  2020feb10hkt2107

Q1. If Win32Image Manager V1.0 gives error message when trying to flash a buster image, what should I do?
A1. Use SD Formatter V4.0 to "Overwrite mode" format the SD card (yes, "Quick format mode" won't do), then the SD card will now be flashable.

Q2. If after SD Formatter V4.0 has "overwrite formatted" the previously Win32ImageManager unflashable SD card, it is now indeed flashable, but
what Windows 10 File Manager originally showed only one drive G:, now confusingly shows two drives G: and H:.  What drive should I flash now then, G: or H:?