I had that happen to one of my old Nuvi 1340T.
Tried it on Win7 and Win 10
Had to try different Garmin cables to get it to update.
Also update to the latest Garmin Express.

I had reported this to Garmin and all they kept asking what was the error.
Had to keep telling them there was no error all Garmin Express did was update the Nuvi 1340T update was successful.
Over and over each time I plugged this Nuvi 1340T into the pc and used Garmin Express the same updates were there.

This went on for days and Garmin did not understand there was no error.

Like I said I tried 4 different Garmin cables and different USB ports.
In the end I have one Garmin cable marked to be used only on this Nuvi and not to use the other cables.

Also I only update the Nuvi 1340T on a Win7 laptop.
All the other Nuvi's updated with no problems at all on my Win10 now Win11 laptop.