Undeniably you are quite correct in that the Saviour is no more to be known in a “fleshly” manner.It is my opinion this same lesson( teaching) regarding a the spiritual seeing of the Christ is what Jesus was showing Mary Magdalene in John 20:17 “Jesus saith unto her,Touch me not;for I am not yet ascended to my Father”
But to me this is the whole point of this thread: Are Roman Catholics taught to look for a literal presence in the " Host"? Yes or no?
The Church teaching on Transubstantiation and the literal Presence is not the subject of discussion in 2 Corinthians and therefore the text you mention has no connection with this matter of faith.
What St. Paul was speaking of in 2 Corinthians 5 has to do with the “new creation,” how the words of Genesis 1:26-27 are now fulfilled in the human race by what Christ has done for us on the Cross.
A new order has been ushered in through Christ’s passion, death, and resurrection. Since then humans can become what original sin prevented them from being in the fullest sense, namely reflections of God, persons who could be said to truly be made in God’s image.
Under sin we are nothing more than products of other humans, products of the “flesh.” Even Christ, though perfect, was once thought of being nothing more than a descendant of King David in the flesh and therefore the Messiah on that basis.
But in reality Jesus was much more. He is the New Creation. He was not merely a human messiah through which a mundane nation would regain its autonomy. Jesus is Son of God, the Second Person of the Most Holy Trinity, and as such Messiah in an innate sense that only the Almighty could make claim to.
In a sense when Christ died all humanity as fleshly descendents of Adam also died. And when Christ rose from the dead all humanity also rose from the dead in a spiritual sense. The era of the New Creation began wherein spiritual realities became more real that fleshly or physical ones.
This is why Paul wrote:
We are convinced that one has died for all; therefore all have died. And Christ died for all, so that those who live might live no longer for themselves, but for him who died and was raised for them.
From now on, therefore, we regard no one from a fleshly point of view; even though we once knew Christ according to the flesh, we know him no longer in that way. So if anyone is in Christ, he is a new creation. The old things have passed away; see, everything has been made new!–2 Corinthians 5:14-17.
This doesn’t mean we don’t believe in the True Presence of our Lord in the Eucharist. We are part of the New Creation, and this does not prevent us from having bodies of flesh. In the same way this text does not speak contrary to our beliefs as Catholics regarding the Eucharist.