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".