Can the scar-tissue be separated from the muscle and not have an indent at the incision sight? (photos)

The fact that you see pulling up when you flex indicates that the pectoral muscle is adherent to the scar capsule, which is the same thing we see with animation deformity and double bubble. The only difference in your case is that the scar is right over the point of attachment. In my experience release of the muscle is not always successful and conversion to the split muscle plane is best. I would be happy to send you a copy of my article on the subject.

Options to correct this include scar
band release (rigottomy) with fat grafting or open release of the scar tissue
between the muscle and skin (capsulotomy).  The first option involves harvesting fat from another part of your body
and grafting it to the scar after the scar has been released with a small
needle.  This option will not require
another incision.  The capsulotomy would
involve making an incision in the fold you already have and releasing the
muscle attachment to the scar.  I would recommend that you consult in person with a board certified
plastic surgeon.

Yes, I do this via rigotomies subdermally with PRP/Fat gratis to correct the indented situation presented here. Seek experts in fat grafting.