“So Jesus was, but is not now, simultaneously fully God and fully man.
Hence it is not heresy to say so.”
Well, that probably depends on your denomination whether they define that as heresy or not, so I don’t know about that.
Strictly speaking of Jesus’ physical form though, He doesn’t inhabit a frail, mortal human body for eternity. The Bible is clear enough about that.
Works for me.
The Church has always believed he is. His body is not frail, however, it is glorified.
This is basic Christian teaching going back to the Apostles, but hey, somebody's always coming up with innovations.