Can I use girls name for boys? Example: Ikhlas

It depends on the name and the culture you live in. You can use Ikhlas for a girl or boy. But many Arabic girl names end with "ah", as in Fatimah or Aishah, and most of these names can only be used for a girl because the -ah is for the feminine in Arabic.

Sometimes a name is used mostly for boys in one country but used in another country mostly for girls. So most of the time it is up to you and your culture.