Excalidraw is a very powerful yet simple to use sketching tool. It allows you to integrate quick sketches, user interface deigns, even simple charts, etc. into your notes in Obsidian.
Search for “Excalidraw” in Community Plugins.
Here’s a link to a 6 part mini series explaining the plugin: Part 1: Intro to Obsidian-Excalidraw - Start a new drawing - YouTube
Here’s the link to the plugin on GitHub: zsviczian/obsidian-excalidraw-plugin: A plugin to edit and view Excalidraw drawings in Obsidian (github.com)