The polls immediately after a debate don't necessarily measure its full impact. Trump's perception as a strongman who dominates his opponents has now been broken with the entire country watching. There's no way to tell how that's going to shape the race moving forward. And the "living in strange times" X factor is how the loss is handled by Trump himself. He may shrug it off and hit the campaign trail harder, or it may have serious effects on what seems to be an already fragile mental state. Again, time will tell.
This was also my takeaway from the debate. Trump looked weak from the jump when he let Harris take the lead in shaking his hand. He was on the defensive all night. All this capped off by a cringe-inducing "I saw people on television talking about it" when fact-checked on the immigrants eating cats and dogs comment (which was also batshit insane enough to lose some of the 67 million watching). Truly an "okay, let's get you to bed, grandpa" moment.
The substance behind his words has never mattered to his supporters, no matter how vile or dissembling, but the vibe absolutely does. They won't turn around and vote for a Black woman, but there has to be a loss of enthusiasm that comes about from this, if not breaking the spell entirely for a few people. He looked old, small, and weird.