OK, hold on.And He did sit down upon His ascension.
But then Stephen later saw Him standing and ready to judge.
Both "standing" and "sitting" in the Greek don't really have anything to do with whether one is upright on his feet or not.
It is more akin to being SET.
You can use either word (standing or sitting) to describe where something is SET.
Both words describe where Christ is SET --- on the right hand of the Father which is in the heavenlies.
We use both words in English the same way.
The vase of flowers is “sitting” (SET) on the table.
The vase of flowers is “standing” (SET) on the table.
It’s not so much about being on or off your feet, as it is about where you are SET.
If you try to make the Greek word for "sitting" mean off your feet, and the Greek word for "standing" mean on your feet ...... you are going to have some problems in other verses where it is used.
Even if you consider "standing" to be on your feet, and "sitting" to be off your feet, it makes no difference in this case because in both instances Christ is in the same place --- the heavenlies.