But the media wasn't interested in reporting on what Harris's positions were, only on whatever Trump said that week. The same as the media wasn't interested in reporting on all the many accomplishments of the Biden administration, despite the headwinds they had to push against.
So most people thought that "no taxes on tips" was a Trump position that differentiated him from Harris.
I don’t think that it was the coverage (or lack of it) that had people associate that policy more with Trump than Harris. I think it is far more likely that Trump announcing it in June and talking about it for two months before Harris announced she also supported the policy in August was what made it seem more a Trump policy than a shared policy. The Democrats were slow to react and so - even if they decided to get on board a couple of months before the election - they were always going to be depicted as playing catchup.
So most people thought that "no taxes on tips" was a Trump position that differentiated him from Harris.