I have a 16GB SD card with 10%FAT32 90%EXT4. I want to get a single disk image file that would contain all of the disc contents. How can I create a disk image of such a disc on Windows 10?
You could use a tool like ImgBurn, it will read a usb to an iso and also write it back.
Perhaps you may find in the Control panel a tool "file history" there on the bottom left by "see also" go to "System Image Backup" and "create a system image" it should create an iso-file.
If you need a backup you could also use backup tools with gui for windows.
Or try the solution above with ImgBurn or CdBurnerXp.