The Garmin ETrex 20x can be connected to a PC via a USB cable, and with this connection, it is possible to manage maps, favorites and tracks.
Connection
Once connected, the GPS will present itself as one or two disks (one for the Garmin itself, and one for any memory card).
Both disks have the same structure:
Garmin
This is the main folder, into which the maps (.img) files are installed.
There are various maps that can be used - a good start is the OpenStreetMap ones, available here. or OpenTopoMap, available here.
Garmin/GPX
This is the folder into which the tracks are stored. Tracks are stored as GPX files. These can be used for recording or following a route, or even used for geotagging photos (with a program such as DigiKam).