Another user already answered that UE5 is for Unreal. But even you are right about how much better are Unity from the version 5.6, i played old games in Unity 5 and didn't have the problems in menus and others things, that is about how the developer did this. But is one of the best hentai games you can find it.This right here explains so much about why the game's menus are so fucked and why development takes so long. UE5 (Unity Engine version 5, I assume?) is like 5 years old, and the dev wants to UPDATE to this and thinks it's the latest version (what?). Unity has been using yearly notation (2017.1, 2017.2, etc) for their versions since 2017 I think. As someone who has developed on Unity since version 4, this is hilarious. Unity is WAY better now than it was on version 5, and lightyears ahead of 4. It's too bad this project most likely won't even import to the better versions of Unity anymore because of how outdated it is.
Or are we really seeing 5 year old notes here?
On the other hand, i think is a big mistake port this to Unreal, at least this game. Is more easy port to the new version of Unity, but im not a game programmer, but port to the same engine, seems more suitable, because unreal is fucking amazing, but more hard than Unity.