Is there a specific tool you use to figure out your design graph, or is it more a 'mind' thing? I know there's some vscode plugins to kinda visualize how code fits together, etc.
C4 modeling would give you the abstract design or system architecture graph, you don't have to do all 4 levels diagram, just do the one that makes sense to you.
If you are doing something simple, you might not need to do any of that but as soon as you are building something of scale with optimal security not doing system designing is like building a skyscraper with no design, well, you know what might go wrong :)