Heteroplatonic is only feeling platonic attraction to people of the "opposite" gender/a dissimilar gender. It is a subcategory of straight. A heteroplatonic person is not "only friends with the opposite gender". Platonic attraction is the intense desire to be close friends with someone specific, also called a squish. Heteroplatonic people only experience this towards people of dissimilar genders.
Flag
The heteroplatonic flag was made by a user who goes by Shawn on October 26, 2020. The alternate flag was created by Beyond-MOGAI-Pride-Flags on Tumblr.[1]