Many different nc file types exists and it is likely that at least some of them can be exported to PNG format either directly, or as some kind of preview.
The most likely candidate for nc to png conversion would be to export of NetCDF based graphics files to PNG format, for which your will have to use some dedicated tool that works with this format.
Another possible way how to convert nc to png, would be some kind of preview of NC 2D CAD files. Certainly not for the purpose of exporting CAD data, but only for the purpose of making picture of the design.
Updated: March 14, 2023