I downloaded some land cover maps from Copernicus. I was able to load the .nc layers into QGIS (3.18.3, Windows64) where they displayed correctly, but no CRS appeared in Properties and I was unable to reproject. A question mark appeared next to the layer in the Layers list - on clicking this, I was invited to set a projection, but setting to WGS84 just made the layer vanish. The documentation files (http://maps.elie.ucl.ac.be/CCI/viewer/download/ESACCI-LC-Ph2-PUGv2_2.0.pdf) describe the projection as follows:
The projection is a Plate-Carrée with a geographic Lat/Long representation based on the WGS84 ellipsoid (Figure 3-5). The Coordinate Reference System (CRS) used for the global LC products is a geographic coordinate system (GCS) based on the World Geodetic System 84 (WGS84) reference ellipsoid and using a Plate Carrée projection. The projection makes use of an equatorial radius (also called semi-major axis) of 6378.14 km and of a polar radius (also called semi-minor axis) of 6356.76 km. The inverse flattening parameter is of 298.26 m. The coordinates are specified in decimal degrees. A complete description of the CRS is given in as an ISO 19111 WKT representation.
How can I fix this, bearing in mind that I've no experience of coding for QGIS...