Didn't work for me either. Uninstalled Edge Chromium and went back to the Edge that came with 10. WB works with this.
I have the latest version of Edge Chromium and the title bars are skinned properly in Windowblinds.
You need to unload Windowblinds by applying the Default theme, add -disable-features=Windows10CustomTitlebar to the end of the target and close Microsoft Edge. Restart Windowblinds and select a skin to use. Start Edge and the title bar should be skinned.
The only problem I have is when using my Surface Pro in tablet form the min/max/close buttons will not take input from a Surface Pen. Nothing happens when tapping with the Surface Pen.