This is a bunch of propaganda. Ukraine wasn't going to join NATO and Russia knew it. Unless you know something I dont about the months before the invasion, it was said actually that Ukraine wasn't going to join NATO. They have been denied over and over.
The "red line" was simply not bending over to Russia completely right before the war, and to not intervene.
INFACT, the "red line" of no Ukraine and NATO dates back decades, and we refused to let Ukraine join NATO because of it. Russia still invaded.