On https://developer.garmin.com/downloads/connect-iq/sdks/sdks.json you can see an incorrect SDK for linux for version 4.0.3
{ "version": "4.0.3", "title": "Connect IQ 4.0.3", "release": "June 2, 2021", "mac": "connectiq-sdk-mac-4.0.3-2021-06-01-b7cc78017.dmg", "windows": "connectiq-sdk-win-4.0.3-2021-06-01-b7cc78017.zip", "linu,x": "connectiq-sdk-lin-4.0.3-2021-06-01-b7cc78017.zip" },
Please note the "Linu comma x".