I really liked your theory , just wanted to say that in the part of
"why Liotte is continuously looping the day is most likely because he either lost his MC in his original world before going mad with grief over losing MC that he searched for ways to bring them back"
i remember in the game liotte says to the mc " since you went missing" so i don't think mc died, but could've, and the photos that liotte have in the backstage that seems to be from cctv angles may add to the mc being missing, i don't know if they were lovers, but maybe knew each other in their childhood?.
Then to the part where we ask liotte why he was doing a tv host, he say is because we were "assigned as the first guest of the show" so definitely Ivan is Nevi and he put them both in this situation, i also think he were the one that put the flyer on the TV since liotte can't leave from inside the tv (i think)
and the fact liotte is a writer too.. idk i feel that the answer is maybe in the itens in the backstage but idk
anyywayy this game was so fun i wished it was longer, definitely obsessed with liotte and his design, he's like a misture of furina and scaramouche design sense like, or maybe lyney? :D