I cannot speak specifically to MCO or TSA requirements, however I can tell you about my experience with a walking boot and Canadian airport security [which for many other things is very similar to US airport security in their requirements].
At the time, per doctor's instructions I was allowed to take the boot off to do things like shower and sleep, but otherwise while doing any walking it was to be on.
Therefore, at security I left the boot on.
At the magnetrometer, I was asked if I could walk without the boot. I said "No". They then asked if I was able to take it off if I am sitting down, and I said "Yes". They said not a problem and explained they have a process I will go through, which will include a pat down.
They had me go through the magnetrometer. It went off. They wanded me. They then did a body pat down. Then they had me sit in a chair and take the walking boot off. BTW, while I was standing for the pat down they asked and made sure I was ok with standing.
They took the walking boot over and put it in a tray and put it through the xray, then swabbed it, then brought it back to me.
While I was seated and they were taking the walking boot for its little journey, they finished the pat down of the area that had been in the boot -- they asked where the injury was and were careful around it. I offered to just take the sock off but they said I didn't have to [probably good for all of us, since it can get pretty stinky in the boot!!].
Then I put the boot on and was cleared to go. As I was putting it on they said no rush, take as much time as I need.
I did ask what happens if the person can't take the boot off, and they said they have a process for that too.
You could contact TSA Cares and ask them what to expect:
https://www.tsa.gov/travel/passenger-support