Omniplatonic refers to someone who regularly feels platonic attraction to all genders, though gender often still plays a role in one's attraction.
Omniplatonic does not refer to someone who simply "has friends of multiple genders" or "is capable of being friends with people 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.
It is the platonic counterpart to omnisexual and omniromantic.
History
It is unknown when the term omniplatonic was first used, though it has been present within queer spaces since at least 2018, when a flag was created for the term.
Flag
The omniplatonic flag was created by Tumblr user beyond-mogai-pride-flags, June 24th 2018.[1]