The game was made with Unity 6, and the player does need to meet Unity 6 requirements. Unfortunately, Windows 8 is not supported by Unity 6 anymore. You can check the requirements on the link below, under the category 'Unity Player' and ' Desktop'.
https://docs.unity3d.com/6000.0/Documentation/Manual/system-requirements.html
Thanks for the report though, it is something I should have added to the description and will do so.