grease pencil strokes to mesh is not available in 2.8 release what just happened it was there in 2.79 beta and 2.8  alpha versions grease pencil strokes which can convert to mesh shortcut key is alt+C just disappeared in the official release or is there any way to convert grease pencil strokes to geometry in new release
You can convert it through the object menu in 3D view while in object mode (Object > Convert to > Polygon Curve). An option to directly convert to a regular mesh object doesn't exist, however you can convert either the polygon curve or the bezier curve to a mesh.