Is this grammatically correct? I’m a hardcore introvert What does it mean?

Yes, the sentence "I’m a hardcore introvert" is grammatically correct. The phrase means that the speaker identifies strongly as an introvert—a person who tends to be more reserved, enjoys solitary activities, and may find social interactions exhausting rather than energizing. The term "hardcore" emphasizes that the speaker feels this introversion is a significant part of their identity, suggesting a deeper or more intense level of introversion.