I use Excalidraw for this kind of stuff. It has the best interface of all the tools in its class and it's easy to create diagrams/flows/mockups that peope recognise are 'in progress', but still look great.
I use excalidraw for almost everything. Brilliant tool. I already mentioned it in another response in this thread but using excalidraw inside obsidian via https://github.com/zsviczian/obsidian-excalidraw-plugin has been a game changer for me.
