Plato did not have "doctrines"
Here : "First, in his Seventh Letter, Plato denies that the tyrant of Syracuse, Dionysius II, and his pseudointellectual courtiers could have known that about which he is serious (περὶ ὧν ἐγὼ σπουδάζω). They could not have understood it, “For there is no writing of mine about these things, nor will there ever be. For it is in no way a spoken thing like other lessons (ῥητὸν γὰρ οὐδαμῶς ἐστιν ὡς ἄλλα μαθήματα) . . . ” (341c1-6). This means not that Plato’s serious insights are secrets that, perhaps, could be divulged esoterically but, rather, that they are ineffable, impossible to encapsulate in either oral or written speech. Accordingly, we must not expect to find propositional truths about ultimate realities in any Platonic text." Strauss got this wrong in thinking that the fact Plato noted that he could not express his deepest insights in his dialogues meant that he had some "esoteric" teaching that was too dangerous to reveal. No: The Tao that can be spoken...