The trick to getting a fresh off the grill burger at McD's (or any fast food joint for that matter) is to ask for a special made-no mayo, or no ketchup, or no tomatoes-it doesn't matter what you omit, just don't order a stock burger. Stock burgers are what sit under the heat lamp.
Sorry, but this is not true.
This USED to be true with McD’s, but hasn’t been for a very long time.
McD’s, went to an assembly line setup like BK, where the burgers are cooked ahead of time and held in a warming tray, and then assembled to order, just like BK.
You are correct that back in the day McD’s would assemble their burgers all a certain way, and then hold them pre made in a holding bin, that is not the case any longer, in nearly all situations. Now the burgers are cooked ahead of time, held in a warming tray and when you order, whether it be a standard or a special order, it is assembled to order using that premade patty.
Now in very busy McD’s or BK’s they may indeed make a certain number of standard burgers ahead of time to help speed service, but you are not getting a fresh off the grill burger when you special order by default... unless you explicitely tell them I WANT IT FRESH OF THE GRILL, that is the ONLY way in a McD’s you will get a fresh burgher.
It takes all of 44 seconds to cook a standard burger, or 1minute 45 seconds to cook a quarter pounder. So, if the place isn’t crazy busy, I will order it that way when I am there, but just ordering it without somehting, or special order doesn’t get you a fresh patty any longer, hasn’t for a decade or more now.