If you are looking for specific (stick fonts) that don't have an "inside" to fill, those are typically labeled as SHX fonts in the LightBurn font list. How to Add a Stroke to Letters in Lightburn

: Click the Preview icon (TV screen) or press Alt + P . If the text appears solid black in the preview, it will be engraved as a solid shape.

: Found in the Cut Settings (double-click the layer). A lower interval (e.g., 0.1 mm) makes the fill look smoother and more solid.