The concept you are referring to seems to be related to wave behavior at the boundaries or endpoints. When a wave encounters a boundary or obstacle, it can undergo a phenomenon called wave reflection. At the point of reflection, the wave temporarily appears to have a shorter wavelength, which is known as the apparent wavelength.
However, it is important to note that the apparent wavelength being shorter than the Planck length is not a well-established or widely accepted concept in physics. The Planck length, denoted by "ℓP," is the scale at which quantum gravitational effects are expected to become significant. It is an extremely small length scale, approximately equal to 1.616 × 10^(-35) meters.
At such small length scales, our current understanding of physics breaks down, and the theories that describe the behavior of particles and waves may not hold. Therefore, it is not meaningful or appropriate to make definitive statements about the behavior of waves and their wavelengths at or below the Planck length.
It is worth mentioning that the Planck length is not directly related to the concept of apparent wavelength during wave reflection. The apparent wavelength depends on the specific conditions and properties of the wave and the reflecting medium or boundary it encounters.