It all seems a bit hit and miss.
My 2023 Crosstar when it's on our drive can't find the router in our house. So I attempted to do an update using a USB. I used the one with all my "car music" on it as there was room. I attempted to download any updates and the site said it could take up to ten minutes. I gave it twenty and it was still uploading! So I called it a day. I also deleted the Honda update connection file.
This was over a week ago.
I was sitting in my car in Sainsbury's car park the other day, with the engine running and the radio on. All of a sudden, a message flashed onto the screen which said it was doing an update. It was over in a few seconds.
Amongst my many music files and playlists, on the USB I have in the car, I noticed this morning there was a file that said "Garmin." Maybe that was used for the update?
In the meantime I'd ordered another Sandisk, they are only seven quid. So tried another upload using this as a dedicated USB.
I did this yesterday and it worked, well, it said the car's software was up to date!