I press or "set" the seam first. Then unfold and press to the dark if possible. Look at the fabric and stitches before pressing and then after pressing. Of course, after pressing, you will see a flatter fabric and flatter seam line.
The same happens when stitching borders. On a side note, I stay stitch and then press again all borders that are added to quilts.
https://www.quiltingcompany.com/8-ti...ms-quilt-tops/