Do i need my old deltarune saves for chapter 5?

steam cloud does back them up, but i'd still copy the folder by hand. cloud sync has overwritten a newer save with an older one for people before, and that's a bad way to lose a chapter 4 ending.

you don't strictly need them, you can start a chapter without an old file and it just gives you a default. but your choices only carry forward if you load from a completed save of the previous chapter, so keep your chapter 4 end save safe. on pc they live in your local appdata folder under DELTARUNE, worth copying somewhere before an update lands.