You don’t want to upload QGIS. You want to download it. Once downloaded…by default, MacOS may play it overly safe and assume it’s Malware - that is if the security settings don’t recognize the developer. There is a setting in Privacy & Security that allows you to bypass this and install apps by ‘unknown’ developers. Use at your own risk of course but if you get an official GIS build from their website…you should be fine.