My External Hard Drive’s format changed to FAT16 without any reason

I have an ADATA HD710 1TB external hard drive which I use mostly in my Mac Mini 2011 and I have created two separate partitions for my drive.

One of the partitions has APFS (Apple File System) format and the other has MS-DOS FAT (FAT32) format. I use the second one for Windows 10 that is installed on my computer using Bootcamp. As it’s not possible to view files of the drive which is formatted in APSF in Windows I use that FAT32 partition to move some files from my main drive to that and view them in Windows.

Yesterday I plugged my external drive in to Windows 10 and after copying some files I just ejected it. Today when I tried to access my files in macOS I realized that my Hard drive’s format is changed to FAT16 and none of the two partitions which I had created are displayed.

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I tried repairing my drive using the Disk Utility’s First Aid feature but it didn’t work. I also tried repairing it via Terminal using diskutil repairDisk command and the result was the same as Disk Utility. Finally, I tried repairing it in Windows (using diskpart commands) and I was unsuccessful again.

How can I fix this issue?

Please notice that I really need the information inside my main partition of the drive (The FAT32 partition is not that important for me). Otherwise, I know that if I erase the whole drive, I can use it again.

The exact error message that I get when I connect my external drive to macOS is:

The disk you inserted was not readable by this computer.