male genitalia vs genital organ

male genitalia and genital organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
male genitalia	Yes	No	No	No
genital organ	Yes	No	No	No

As nouns, genital organ is a hypernym of male genitalia; that is, genital organ is a word with a broader meaning than male genitalia:

Other hypernyms of male genitalia include crotch, genitalia, genitals, private parts, privates.

male genitalia (noun)	genital organ (noun)
external male sex organs	external sex organ