Xenosexual from xeno, a prefix that represents strangeness, foreign + sexual is a sexuality toward humanoid and possibly not humans. It's the fantasy of having a relationship consentual with an alien species.
In the past this term was refering to white people having a relationship with an none White. Today this term isn't really used anymore and was reapropriate only recently.
There is not know flag of xenosexuality.
There is no known flag for xenosexuality.