ok i know im late to this but there is so much to disprove what bullshit you just said. TOBY FOX HIMSELF SAID "I will say basically, what you are seeing here [deltarune] is not undertale.
To rephrase that, deltarune's world is a different one. With different characters, that have lived different lives. A whole new story will happen." even if he didnt say that, Asriel is in college. in undertale hes just a kid. This cant be after Undertale because, 1. undyne has 2 eyes. 2. undyne doesnt know alphys and vice versa. 3. there is no mention of asgore being a former king, or a king right now in Deltarune (he owns a flower shop). deltarune. is. an. alternate. universe. end of story.