Just did it dude, what a rush. I got to radiance 4 times before being able to kill him, it's pretty intense having to clutch it after 43 bosses. That final ascent dodging the beams is wild.
Clip of the last two fights. I absolutely love the Vessel encounter, one of my favorite bosses ever.
Congrats! Getting the platinum in Hollow Knight is the most challenging thing I've done in a game I think.