use jinja2 context variable within MarkDown figure block

Question

I am trying to use a context variable that is rendered at runtime within the LaTeX/MarkDown code block that generates a figure. In principle, I would like to allow for dynamic paths to the images to include in the figure.

This is a working piece of code:

\begin{figure}
  \centering
     \IfFileExists{path/to/my_image.png}
     {\includegraphics[width=0.9\textwidth]{path/to/my_image.png}
     {\includegraphics[width=0.2\textwidth]{path/to/image_not_available.png}
     \caption{My caption.}
     \label{Figure.1}
\end{figure}

Now, I have a context variable which I set at runtime:

Path to the image folders: {{images_folder}}

This works in "plain" MarkDown, but I cannot find a way to use this variable within the figure code block. I tried (with no success):

 {\includegraphics[width=0.9\textwidth]{{{images_folder}}/my_image.png}
or
{\includegraphics[width=0.9\textwidth]{'{{images_folder}}'/my_image.png}

Do I need to somehow escape the {{ }} construct or? Can you please give some advice? Thank you

EDIT: to give a bit more insight as @Marijn requested wrt the sequence of steps:

1. I am using a JSON file as input in the Python module that handles all the data ETL and context rendering
2. Once the data is parsed and loaded into a dictionary, a RenderContext object is initialized with all the metadata and data to populate all the context variables used throughout the report that is generated.
3. These variables are then fed from the RenderContext dictionary into the MarkDown templates, based on their specific key (i.e., the RenderContext <key,value> pair "number": 10 becomes {{number}} in the MarkDown plain text.
4. I also have a header.txt file for the front page where I got entries such as `title: "This is a report about {{title}}" and date: "{{date}}"
5. I have also tried to add \graphicspath{{path/to/images}} in my main .tex file but for some reason this gets ignored.
6. I have also tried to add to the .tex file the environment variable that hosts this path (e.g., IMAGES="/absolute/path/to/images/" following this post but with no success. Does not want to recognize the newly defined command.

As mentioned, in plain MarkDown text, I can access the variables just fine, but when it comes to figure or table blocks, I cannot make it retrieve the variable value. I have also tried with \includegraphics[width=.....]{$images_folder$} as i saw it implemented in the main .tex template, tried to escape it with \ etc.. etc.. but no success.

An example of a plain MarkDown text using one Jinja context variable would be:

This sample was found to have a contamination of {{contamination or '\\notset'}}.

where if this key,value pair for contamination is not found in RenderContext, I would display a custom [not_set] text in red to make me aware that something goes wrong.

Thanks again for the help!