The ornamental design for a floatingplatform, as shown and described.
FIG. 1 is a top perspective view of a floating platform;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a left and right side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is top view thereof; and,
FIG. 7 is a bottom view thereof.
The shading lines shown in the drawing represent the three-dimensional contour of the claimed design, and are not intended to indicate surface decoration.