Depending on what it is it could be just more compressed as liters is volume but oz is weight. That said they’re both 96 grams so the only thing that “makes sense” is if one was weighed under different gravity
... Or the specific density of the material inside the can is different.
The old formulation was more dense, so it weighed more at the same volume.
Or the volume (in mL) is the volume of the can, and not the uncompressed volume of the marital inside the can, and they just lowered the pressure of the substance inside the can as shrinkflation.