To open data files in NetCDF format - which is the case for most Copernicus datasets - in QGIS, you will need a QGIS Plugin CMEMS-NetCDF. Developed in the context of the Copernicus Marine Service and available for free. Access the link below to download the plugin.
To open NetCDF files, which is the file format of Copernicus Marine
Service products, in QGIS you will need to download the Copernicus
Marine Service QGIS Plugin CMEMS-NetCDF