  Owing to the broad energy coverage of Insight-HXMT in the hard X-ray band, we
detected the highest energy of pulsation exceeding 200 keV around the 2017-2018
outburst peak of the first Galactic pulsating ultraluminous X-ray source (PULX)
Swift J0243.6+6124, which is the highest energy detected from PULXs to date. We
also obtained the highest energy of pulsation of every exposure during the
outburst in 2017-2018, and found the highest energy is roughly positively
correlated with luminosity. Using our newly developed method, we identified the
critical luminosity being $4\times 10^{38}\, \rm erg\,s^{-1}$ when the main
peaks of the low and high energy pulse profiles became aligned, which separates
the fan-beam dominated and pencil-beam dominated accretion regimes. Above the
critical luminosity, the phase of the main peak shifted gradually from 0.5 to
0.8 until the outburst peak in all energy bands is reached, which is in
agreement with the phase shift found previously at low energies. Our result is
consistent with what is derived from spectral analysis.
