Hello cinnabarin,

There's a known issue related to running Mac games using Wineskin such as Sniper Elite: Berlin 1945 on macOS 10.13 High Sierra. We are working on fixing these games, but it's an ongoing effort and I cannot give you any estimates when this work will be finished.

Right now, you can try the workaround described here: http://wineskin.urgesoftware.com/tiki-view_blog_post.php?postId=87

If you will need any further assistance, please contact our customer support: https://support.gog.com