If Stipe wants to win this fight, he has to bring more than a right hand. His right hand has been good enough to beat nearly everyone in his path up to this point. His right hand wasn't enough for Ngannou, but he used take downs to gain the edge. Any time Stipe wanted to get Ngannou to the ground or needed to get him to the ground, he did. Stipe has a big frame, and good hand/eye, but his defensive boxing isn't by the book. He almost always uses his reach, not head movement or parries, to avoid punches. Stipe did show improved head movement against Ngannou (mostly ducking and turning) but reverted to previous tendencies during the DC fight (in and out).
DC leaned away, turned or basically blocked every right straight thrown at his head. DC is smart; he knows Stipe's only weapon is the right hand. When Stipe needs to get the DC fight to the ground, he doesn't have the wrestling option.
Stipe needs to work his jab, the right to the body, and his kicks. Jon was able do beat DC using variety. Right now, that's the only successful blue print on defeating DC.