I’m sorry but I’m not satisfied with your answer.
We already know that a function cannot access files outside of its folder…
Have you read the first attached article?
I copy literally:
One option is to tell our build system the paths of any additional files that should be included in the function deployment. This can be done in the netlify.toml configuration file using the included_files property of the functions block,
(extract from How to Include Files in Netlify Serverless Functions)
Reading this I understand that by setting the included_files parameter the system will copy the selected files to the function folder automatically in the function deployment.
I copy the end of the article (literally):
You can include any type of file in your serverless functions, even if you reference them using dynamic expressions. You can add these files manually in your configuration file...
We think the author (@eduardoboucas) explains it clearly. Modifying the netlify.toml configuration you can automate the adding of any file in the deploy of your function.