Sourdough

Hello! I'm attempting to make the sourdough that Jacob shows in his video. I have a good starter that is at 100% hydration, and it passes the float test. I weighed all my ingredients. I hand kneaded my dough for about 20 minutes, and the whole time, the dough felt quite stiff. In the video, the dough looks nice and soft, and it looks like it stretches easily during the slap and fold. Even during my stretch and fold, the dough was stiff and it was much more work to make it happen. I'm at the rise before the final proofing and while it's risen well, it still feels stiff.