You no longer need to use resources.ExecuteAsTemplate to pass values from your templates into Sass files. See:
https://discourse.gohugo.io/t/initialize-sass-variables-from-hugo-templates/42053
Clone the example at the bottom of the post. Among other things, this example sets the body background image to the .RelPermalink of an image that has been processed by Hugo. In the example, see:
layouts/partials/get-scss-vars.html.