We maintained a c4 model of our systems built for importing and displaying on structurizr.com and tbh, it wasn't fun. You don't get the same intuitive understanding and overview from the code that you get from a diagram and there was no fast local preview. You had to upload your code to the server.
Even worse was the fact that adding a new box usually meant realigning all arrows. As a consequence the diagrams were never kept up to date on a continuous basis.
I had a better experience using plantML for sequence diagrams. The task is easier so the output of the interpreter is typically useful without manual interventions.
FWIW You can do a C4 model using plantUML diagrams [1] imported directly into RST markdown (or inline, fwiw, but that makes live preview harder)
That way in an editor like VS Code (e.g. where you have/make plugins to support) you can live preview the diagram in your editor while editing the related text - both get syntax highlighting etc. Using a tool like sphinx to tie everything together helps, as you can easily (enough) write extensions to handle quirks of your own setup reasonable if needed.
I've seen this work pretty well, in a /doc folder in the git repo with some autogenerated reference links as well, from the same repo. You either need the plantUML jar file local (and java, obv) or to point it at a rendering instance "local enough".
I had a better experience using plantML for sequence diagrams. The task is easier so the output of the interpreter is typically useful without manual interventions.