It’s a ~6 months old Retro Gaming Cables PlayStation 2 RGB SCART PACKAPUNCH PRO with sync on luma.
I remembered that I have an old Xbox Advanced SCART cable. I’m going to switch that over to output YPbPr instead. That way I can at least test AV1 YPbPr with another cable. There is a way to make the Xbox output RGsB, but I don’t feel like messing with that if I don’t need to.