As of right now, applying variables to stroke is incredibly counterintuitive. Right-click → apply variable. Why not use the same pattern that was used everywhere else? Cog.

A second thing that would be incredibly useful would be to have the stroke property exposed and overrideable. This is incredibly useful when you need to have icons with different stroke sizes. Instead of having to create 5 variants, you can create a single one, scale it based on your needs, and simply override the variable attached with a different stroke size.

This would also save a lot of memory for situations where you have large icons sets that are part of the design system.