Is it possible to solve a magic square made up of a system of unknown symbols?

No. I could populate a 9×9 magic square with the letters A through I. You would never figure out what numbers were represented by the letters because a 9×9 magic square is not unique.

Any magic square has multiple solutions in the sense that you can turn one solution into others by rotating 90, 180 or 270 degrees or by reflecting horizontally, vertically or along the diagonals.

For a 3 by 3 magic square you would know the value in the middle, which has to be 5.

Are the symbols invisible??