Arguably it was a blip. The poll taken after the debate showed that he lost about 2% and Trump gained about 1%. People have decided who they will vote for and there isn’t much that can change their minds. That actually is a good thing. It makes it less likely Biden will be replaced.
The Biden meltdown is something the public had not seen so clearly before. If a 2% drop in polls corresponds to the actual vote in November, only 2% of the voters care if the person entrusted with making decisions about a nuclear attack can communicate verbally.