That was indeed a thing several years ago as ad networks were being forced to support HTTPS, but all of the major ad networks and ad servers have supported HTTPS for years at this point.
I don't doubt there are some bespoke ad servers or other dark corners of ad infrastructure where HTTPS support is still lacking, but that should be rare at this point.
I don't doubt there are some bespoke ad servers or other dark corners of ad infrastructure where HTTPS support is still lacking, but that should be rare at this point.