Having been there, done that with ankle surgery and traveling with a franken-boot......

Even if your boot has no metal in it where it will not alarm the WTMD, expect a secondary screening consisting of a visual inspection and an ETD swab of the boot (and perhaps your hands and other shoe as well) along with perhaps a full body patdown.

Now in line with that....

If requested to go thru a NoS, opt-out (even if you have decided in the past that it's ok to go thru a NoS) as you don't know what type of "anomalies" will show up because of the boot

Do not take your boot off or even open it up to show the TSO that there is nothing "artfully concealed" in side it-period! Even if you alarm, let the TSO do their job and resolve the alarm as you are not required to remove the boot. Also, do not take off your other shoe when going thru the WTMD and if "told" by the TSO you have to remove your shoe, politely tell them "no thank you as that makes me unsteady on my feet and I don't want to fall over"