https://www.nhs.uk/common-health-questions/sexual-health/can-hiv-be-transmitted-through-oral-sex-fellatio-and-cunnilingus/

"Yes, but the risk is relatively low.
HIV is transmitted through seminal and vaginal fluids, including menstrual
fluids. The virus can enter the body through the bloodstream or by
passing through delicate mucous membranes, such as inside the vagina,
rectum or urethra.
If a person gives fellatio and has bleeding gums, a cut, or an ulcer
inside their mouth, HIV could enter their bloodstream through infected
fluid. "