UE4 version is pretty much a vertical slice of theirs, while UE5 is the end product they want to have as a finale, slowly buidling it up with a lot of detail.
You can play UE4 version to see the game as a pitched concept - it has many sex opportunities, some story with quests, working solid combat, dungeons. Ultimately it doesn't feel like a truly united project that leads somewhere but currently it has 4xTimes more content than UE5. At some point it kind of just ends (naturally) leaving you wanting more.
Is it much different to UE5? In general UE4 feels like the same project that prioritizes quantity over quality in comparison to UE5 but it's still a solid 3D indie unfinished game.
Unlike UE5 though UE4 has sex scenes with a Naga, with a Void being, with a Centaur and with a Wyvern (feral dragon). Which are the biggest differences that matter imo. I would suggest to try it even if just to experience these opportunities.