i mean if there is not a dm feature (i think) but if you feel like "i'm not like other girls" kind , there are encryption methods that need a key to give a correct output, so you can do that if you want
E: [ However , i heard that the itch.io pages (at least the product ones , are very customizable so I'reckon you could make some comment box on your profile like in steam.
maybe you even could make it so nobody else sees the comments , only you. No idea. Never read their documentation , if they have one]