Ah, very sorry for the inconvenience. I read the twine guide on submitting to itch and they mentioned something about making sure the Story Format works on mobile before choosing that option.
To be on the safe side, I didn’t toggle the option. But I guess I should’ve checked if the story format I used, Harlowe, supports mobile before I default to not checking the option. I will also look into the portrait alignment when I update the build.
Lesson learned and thank you for bringing that to my attention.