@HeadNorth are you an abuser? You’re definitely acting like a bully at the very least. Most decent grown-up kids wouldn’t want an abusive parent anywhere near their graduation. It’s meant to be a day of celebration with people who actually love you, not a day of fear with people who are invited out of a warped sense of responsibility.
I wouldn’t have had my dad in 100 miles of my graduation or wedding if he’d abused my mum. Because guess what? I love my mum and her being ok would 100% trump me feeling the need to have both biological parents witness my graduation.
OP, your situation is very different, although I do sympathise. Some good suggestions here - keep things brief, have a good read of the leaflet, chat to other parents, go to the loo, go to get a drink. When DC is there, just focus all talk to them, and keep it positive. “Darling, congratulations, you’ve done so well, I’m so happy for you! Were you nervous going up on stage? What have you got planned with your friends later? Would you like me to take a group photo of you with your flatmates/ course mates etc?”
if dc ask you to be in a photo together, just make sure DC is in the middle then you can pretend it’s just you and them in your head, and make sure you just think of your pride for their achievement, so you can give a proper smile. Good luck, you can do it - the anticipation is usually much worse than the reality.