Is it obligatory to make up missed prayers while sitting during a treatment period that prevents prostration, or should one wait until recovery to make them up?

The prayers you missed while healthy must be made up now according to your ability. Your inability to prostrate does not permit you to pray while sitting; rather, you must pray standing, then bow, and after rising from bowing, sit and gesture for prostration with your head.

You must also make up the prayers you performed sitting while you were able to stand. Do not occupy yourself with supererogatory prayers while you have missed obligatory ones.