You cannot import GPX files directly to the Garmin Venu 4. Instead, you can manage the routes via the Garmin Connect app or other third-party apps and transfer them to the watch. The Swisstopo app itself may not support direct transfer to Garmin devices, but you can export the routes in GPX format and then import them via Garmin Connect.

venu 4 cannot display map, if you need map you need for example garmin fenix