Gregory Douglas said:
I'm using Windows 10 version 1909. If I want to make a system image, can I format the external drive using NTFS, FAT32 or exFAT? Do all three formats work?

If you use Macrium Reflect then any format will do, though ntfs would be more convenient. For Fat32 Macrium will automatically split the image into multiple files, each one less than the 4GB Fat32 file size limit, on ntfs you'll get a single large image file.

If you mean the built in Windows system imaging, then it HAS to be ntfs - it can't work with anything else. But then, as Microsoft say, you shouldn't be using it...

Microsoft said:
System Image Backup (SIB) Solution
We recommend that users use full-disk backup solutions from other vendors.
Features removed or Deprecated in Windows 10 Fall Creators Update