There is no private or public direct message system on itch. Wich in my opinion differentiates it from the usual social media sites.
The reasons for this are another topic, but if you put a message option on each account's profile, you suddenly have this kind of message option.
Also, if you have questions to discuss, that are not related to a published project and can't be asked on the comment section of that project or any devlog, those questions probably should not be asked on itch in the first place.
Creators that do want to be contacted, can link to their social media or discord or other contact info. They usually do not need nor want yet another channel to collect unsolicitated messages.