The president cannot force military personnel to undergo medical treatments irrespective of the medical or operational necessity.
No, you obviously don't get it. Military personnel are not lab rats. Their rights are limited, not nonexistent, as you seem to believe.You obviously don't get it, which is why it a good thing you are no longer in the service. Orders don't have to be "justified". They sure as Hell don't have to be justified to some E3 or E4 or whatever you were.
Military personnel still have the right to exercise sovereignty over their own medical decisions. The president cannot simply order them to undergo medical procedures willy-nilly. There has to be a legitimate medical or operational justification, otherwise it's not a lawful order. Biden cannot just wake up tomorrow and order the entire military to eat 10 aspirins just because. Similarly, he cannot just decide that everyone in the military must inject themselves with a COVID shot just because. He needs an actual lawful pretext for the order beyond simply being the president.