I don't use AI for that, but frequently illustrate things in Figma (even flowcharts and architectural diagrams, etc.).
It's just a nice UI, fast, and it's easier to keep everything in one place vs spreading it out over GDrive/third-party flowchart apps, etc., especially if the people you're sharing with are also Figma users.
When Figma is too much work, honestly, just having an dry-erase whiteboard near the desk works wonders for visual thinking and in-person meetings.