The following examples shows four GPX tracks on a map.
Each track has a different color. All tracks have the same, default line width. But this could be changed per track. All tracks are shown initially but can be disabled in the layer switcher.
GPX file handling
The GPX tracks have been recorded with the "Stadtradeln" app. To reduce the size of the tracks, I used gpsbabel with the following command:
gpsbabel -i gpx -f recorded.gpx -x position,distance=5m -o gpx -F rad-2023-05-23.gpx