I think there's actually a lot of undecideds out there, though not really in a traditional sense.
The biggest bloc is people who hate Trump as a person, but feel like Harris would be a disaster. A lot of those people may just not vote, but they are gettable by either campaign with the right persuasion. The Harris campaign has been pushing hard to get these people and it's not really working, in part because Harris is so bad at retail politics and she isn't improving.
I loved that turn of words, “Retail politics”. I think your post also nails it.