Hair before, thicker in the royal family and the Zoom call (wouldn't look as good and full if straight).
I don't think James, Carol and Pippa have good hair. Michael does though and George seems to favour/resemble him the most. Kate's hair has definitely improved since she's been in the Royal family.
It could be down to great products, care and blow dries/stylists/cuts and perhaps the occasional hair piece, clip in, nets, etc. It was definitely thinner looking in the past, less body.
She did a good job on her hair in the Zoom call, but remember it will look thicker as it shorter and curled/blow dried. Both of which make the hair look thicker and with more volume/lift/body.
Whatever Kate's secret is, her hair looks good to great most of the time.