Panplatonic does not refer to someone who simply "has friends of multiple genders" or "is capable of being friends with individuals of any gender", rather it describes someone who regularly experiences squishes or "friend crushes" or otherwise feels a strong desire to be friends with someone in particular.
The panplatonic flag was designed by Disneyfan1413 and was posted on July 15, 2020. The flag uses the pansexual flag with a faded diamond. It was chosen because a faded heart is usually used for romantic attraction flags. The choice of a diamond is potentially in reference to the concept moirails (a form of strong platonic relationship) from Homestuck.
Another panplatonic flag was created by an anonymous submitter to beyond-mogai-pride-flags on July 31, 2017. This flag has no known meaning.
The second alternate flag was made by FANDOM user SakuraFeathers. Pink represents femininity, purple represents androgyny, blue represents masculinity, yellow represents nonbinary, white represents other genders, grey represents demi/grey genders, black represents genderlessness, and the emblem, a yellow rose, represents friendship.
The third and fourth alternate Panplatonic Flags were made by FANDOM user KateXya on September 4th, 2021. The added gradients to the original and updated pansexual flags depict the diversity within the Pan community and the white flower in the center represents friendship.