The backup crashed at about 22 GB.
That usually means eM Client detected an error in a message or messages and couldn’t then continue.
Try closing eM Client and then “manually running the database repair” as per @garys post below and then try running the backup again. Sometimes that can fix it if it is a database error.
Also suggest to “reboot your computer before running the backup again”, just incase there was possibly a resident program that may have been running and might have interfered with eM Client.
Note:- I had the backup stop once when eg: a friend of mine imported 1000’s of old Outlook messages into her eM Client where some of the messages were corrupted with eg: weird hieroglyphics in some emails. I had to delete those corrupted messages to then get the backup working. So if the backup still stops, then could be there is possibly some corrupted messages.