Hey, sorry to hear this!
I haven't actually tried running this through the itch.io app, so that may have something to do with it.
Try just downloading the .rar file and exporting all the files somewhere, and then executing the game's executable.
For most people, the game is super laggy because of either anti-virus options, graphic card manager options or just because they are executing the game inside the rar file.
Let me know if any of this helps!