After looking through the profile you mentioned here is the post where it is first mentioned. It is elaborated on a few posts after this one.
Just based on how genetics work a homozygous form is always possible (excluding unusual cases like a lethal super) and it will always pass on one copy of a gene. Debating if supers are possible in simple dominant traits isn’t the purpose of this thread so I’m not going to elaborate further. But, if you want to discuss this further feel free to create a new topic about it.