The Navman F20 uses a proprietary USB protocol, not standard mass storage. The official drivers from Navman/ MiTac were signed for Windows XP/Vista (32-bit). Windows 7 (especially 64-bit) often rejects them due to driver signing or outright incompatibility.
Since the Navman F20 is a legacy device (circa mid-2000s) that was designed for Windows XP, Windows 7 requires specific troubleshooting. Help/Guide: Getting Navman F20 to connect to Windows 7 (Driver fix) driver navman f20 windows 7
After a lot of trial and error, I wanted to share what worked (and ask for advice if anyone has a better solution). The Navman F20 uses a proprietary USB protocol,