If the president, as a citizen, requests an experimental treatment for compassionate use, that should be considered the same as anyone else.
The difference here is that the president would clearly be abusing his office to get the treatment, and this should be disclosed in his medical evaluations.
I think also many other people than the president should have preferential treatment when it comes to certain things. If it's about health, yes, the president should be able to cut the "line". If it's about renewing a driver license or other petty things, of course as well, that should be straight cutting line, you wouldn't expect a president to waste his time standing in line anywhere.
I'm not from the US but to me it seems just normal to not compare a rando with the president, especially if it doesn't hurt anyone else.
Imagine if we had an experimental drug that would genuinely make people "smarter", why wouldn't you want the president to immediately access it, it can benefit the nation.
He may have medical conditions that have not been disclosed, but it does not seem like he is seriously ill or in a situation of imminent death, so this would appear to be an abuse of the system.
Doctors abuse the system all the time for their own benefits [1], you think that if a family member has some issues, they won't prescribe him drugs illegally without consult? Of course they would.
[1] https://link.springer.com/article/10.1186/s12875-022-01631-z
===
You wouldn't give leftover prescription drugs to a friend asking? I did, they did, seems common.