Could you tell me more about the fullscreen issue? You're the second player reporting this but I've never encountered it on Windows or SteamDeck. How is the window "going crazy", what's happening precisely? And could I ask you what OS you have and what's your monitor resolution? Thanks! :)
I don't know much about Deltarune as I've never played it, but considering Aereven was first conceived around 2004 and this game was released in 2020, any resemblance is purely coincidental (or... Toby Fox plays my games?! ;p)