renderdoc.dll is missing on releases: Gigi-0.991.0.x64.windows.installer.exe and Gigi-0.991.0.x64.windows.zip
Manual downloading renderdoc.dll from the source into the Gigi root folder is required.

Also, FYI, in my case, I need to run GigiViewer as an administrator to capture the frame successfully.
Otherwise, RenderDoc opens with empty captures.