Outline a design
Add an outline on its own layer and keep the design underneath.
Needs a paid plan.
Add an outline
Choose Chart › Outline…. Choose the whole design, every shape or a selection. Check the suggested background and outline color; change either if needed. Set thickness and check the canvas preview, then choose Add outline.
The outline gets its own layer. Undo removes it. Use Edit outline to change it later, or Update after changing the design underneath. Outlining by hand is free.
If the outline looks wrong
Check which color is treated as the background and whether the selection covers your design. Cancel leaves the chart unchanged. On stitches that are not square, check the real-size preview; you can choose to count blocks instead.