Find the highlighted Vëlosummer 2021 routes on your Garmin device; the layer includes all routes and links. Get the file here (if needed, right click and Save Link As…), and copy velosummer.img to the folder Garmin on your device. Tested on a Garmin Edge 1000 and 1030plus.

If you’re using a recent firmware, make sure that you are using the Classic” map theme (and not high contrast or mountain biking).