Queer is an umbrella term for an identity which is different from the social norm, that is cisgender and heterosexuality. Anyone with a different identity can call themselves queer. It can be in terms of gender identity, gender expression, sexual orientation or sexual identity.
Sources:
https://www.medicalnewstoday.com/articles/what-does-queer-mean
https://www.healthline.com/health/am-i-queer-enough#who-its-for