... aaand once more with the debunked "Sol Invictus" garbage.
Christians often appropriated various pagan symbols and Christianized them. When the Roman Empire became Christian, it was common to portray Our Lord as the "Sol Invictus". Here's a mosaic of Our Lord as "Sol Invictus" in a Christian tomb beneath St. Peter's basilica.

It's not unlike how the Christians converted pagan temples into churches, put crosses on top of pagan obselisks, and even when they appropriated the Christmas tree. Our Lord was often symbolized by the sun in the early Church, and Masses were offered facing the sun at sunrise, representing the light of Christ entering the world.
+Vigano is not above reproach, but this nonsense muddies the waters, so that even if there's room for legitimate criticism, it gets lost in the noise.
So mote it be ...
