From Julia Alexander at Polygon:
“It was never in the plan for me to direct Episode IX,” Johnson said. “I don’t know what’s going to happen with it. I’m not sure what’s going to happen with it. I was entirely focused on Episode VIII and having this experience and now I’m just thinking about putting the movie out there and seeing how the audience responds to it. So now I’m not really thinking about that right now."
It's not a no, but it's also not a yes.