Disc of front brake rubs under force
Flex causes this and it's not going to hurt anything. However, it's frequently the case flex is just the contributing factor that pushes the system into rubbing.

Look down at the gap between your rotor and pads, and slowly spin the wheel. If you were to see consistent .2-.4mm-ish gap on both sides, a true rotor (no warbles), and good parallelism between the pad and rotor, there's not really anything you could do to improve things at that point, and you'd know it was just flex causing the rub.

If you see an out of true rotor, off-center pads, or very minimal gap all around, then that means the rotor is getting closer to the pads in certain spots than it should be able to, and while it may not rub unloaded (in the stand etc), adding flex is getting it there. So to solve it you may need to true the rotor, face the frame/fork, reset the pistons, and/or adjust the caliper position.