If you are only backing up a small portion of files on a partition, you should use file backup instead of disk backup, because the file filtering feature of disk backup will emulate the deletion of the files to be excluded from the drive before the backup starts, which will definitely take some time. Overall it should be used to exclude a small number of files from a disk backup, and certainly shouldn't take that long, and we'll improve it in future releases.
Strangely it didn't take too long (Excluding files took about 2~4minutes, A Windows 10 desktop computer, a Windows 11 notebook, and a Windows 11 virtual machine) to exclude C:\Windows on my computers.
Strangely it didn't take too long (Excluding files took about 2~4minutes, A Windows 10 desktop computer, a Windows 11 notebook, and a Windows 11 virtual machine) to exclude C:\Windows on my computers.