Buggender is a xenogender or neurogender that is highly connected to bear, specifically bear cubs. It may be used by someone who species regresses, but it doesn't have to be.
Flag
The flags for cubgender was made by 'byleth' (@hwaisle) on Twitter, on October 8, 2020.[1]
The flags for cubgender was made by 'starchild⁷' (@bangtansboyfie) on Twitter, on August 19, 2020.[2]