I think it is some kind of fungus/mold.
I would remove the two side branches. Then dab the wound with trichoderma.
If you don’t have trichoderma. I would recommend reducing the stress but cutting the stem off about an inch above the rotting spot. You have enough branches and your air is dry. So cutting a couple of branches off to save the plant should be okay.
Pray that the rot had not spread to the core of main stem. Good luck.
thanks for the answers. its such a massive plant. those two branches are huge.
Stress is an interesting view point. I thought it could of been a beetle
I cannot see the pic very week, but it just looks like scarring... the plant had stress there and over compensated. Doesn’t look like mold or anything. Good luck. ✌️🏻💚🌿