Mr. Yanklowitz has openly and publicly expressed apikorsus’ opinions. Even if he had converted with a real frum beis din (who obviously was unaware that he was an apikorus), his purported conversion would be invalid as no conversion can be valid on a person who holds heretical views.
Rav Elyashiv went as far as saying that if at the time of conversion a person believed the world is older than 6000 years, he remains a goy despite converting in the mikva. Even if someone disagrees about the 6000 years point being an invalidating view, clearly an open apikorus cannot validly convert.
Given all that on top of “converting” with a non-frum “beit din” of the heretical OO movement, Yanklowitz is a gentile.