According to a comment about a day ago here, the devs supposedly said on Discord that the itch.io version of the game is no longer being supported. Haven't seen any official source for that myself, but given the existence of an error saying that, it would seem logical that they would only put an "unsupported version" message into the code if they intended to stop supporting something.
I've contacted them using the email address I was given by the itch.io support page (us@innersloth.com). That got an automated "we've received your message" reply straight away, but it's been almost 4 days since I sent the message without a reply yet.
I've seen mention of a different email address being used by support (support@innersloth.com) in the comments here as well, and have re-sent my email to that address today. Hopefully one of these messages will get a response soon.