Top stitched seam is useful in anti-fray and finishing raw edge. Top stitched seam is often used in slit.
Making of Top stitched seam
Sew the 2 fabrics with right side together, and press seam allowances open.
Then fold the seam allowances in half.
Sew the 2mm line from the edge. It’s done.
Right side of fabric is like this. Just sewed lines are visible.
Top stitched seam, movie is the following.