I don't own a TomTom and can't really offer much help.
Have you tried a hard reset?
From the manual:
"To reset your ONE XL, use a straightened paper clip, or something similar, to
push the reset button. The reset button is next to the memory card slot on the
bottom of your ONE XL. Then turn your ONE XL on."
From elsewhere on the web: - BACK UP your SD card first if you use one.
"Carried out a full reset of the TomTom (using instructions from TomTom themselves: remove the card, hold reset button down for 30 seconds, then hold down the power button for 20 seconds, then reinsert the card). Formatted the SD card."
Have you tried to update again just in case your first attempt was corrupted, interrupted in some way or there may even be a further missed patch?
40° 52' 33"S 175° 4' 17"E - 42.521m