Lily frozen after installing 12.20

So, my wife's Lily doesn't work anymore. It started today after the 12.20 update.

It goes like this:

1. It shows the Garmin Express screen

2. I connect it to Garmin Express through the usb cable to my PC (Windows 10)

3. It says "Synchornizing" for about 5-10 minutes, before finally letting me know that "You're updated"

4. I then remove the watch from the usb cable. I tried all sorts of combinations of closing Garmin Express and removing usb-devices before removing the watch

5. No matter which method I choose, the watch first shows the triangle for a few seconds, and then the Germin Express screen, and I can go back to step 1.

The watch doesn't react to presses or tabs on the screen, not shakes or anything else. It's basically bricked, but with the light on.

What can I do? Thanks in advance.

Kurt