Kamala Harris has consistently received lower favorabilities than Joe Biden. In a poll, a plurality of 52% approves of Biden with a net approval rating of 7 points while another plurality of 47% disapproves of Harris with a net disapproval of 2 points.
I have seen people attribute this to the fact that she is a black and Asian mixed race woman who just entered politics a decade or so ago while Joe Biden is an established older white man. Another thing that I think is more relevant is that Harris apparently talks a lot less and sometimes comes across as cold.
I understand that this question could come across as being biased towards Vice President Harris. But Hillary Clinton had many of the same problems, though not as a woman of color. Clinton was seen as dishonest, "crooked", etc.