Is there a relation between hiv and dandruff/seb derm? i have googled it and it's full of such articles that seb derm could be an early sign of hiv? how true is that? too frightened with my severe dandruff on scalp?

If you have not had sex no worries. I you have get tested for HIV would be best. If negative always use protection and ask partners their HIV status or demand a test.

HIV infection is known to worsen seborrheic dermatitis, but is only to be suspected in individuals with high risk sexual behavior. Or in other words, if you are worried about getting infected following a high risk sexual encounter you should test, if no high risk sexual activity, see your doc to escalate treatment for seborrheic dermatitis that can be affected by a variety of other factors.

Get tested. 4th gen HIV test would provide reliable results. If you have not had sex with other men, or commercial sex workers, you would not be at high for getting HIV, Get HPV, Flu and Covid vaccines. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines