Bret likes Kamala, at least has complimented her several times, and he doesn't like Trump who he has never said anything good about.
Bret said straight up there would be no hanky panky or manipulation with this interview and he would decide what was asked. I do suspect there was some behind the scenes interaction with Kamala and/or her campaign which is why she agreed to go on Fox.
And the interview was taped in advance, edited and is currently being aired. (I haven't tuned in yet but am recording it.) I do not have full confidence in Bret's integrity most due to cautionary instincts kicking in, but he may do a good interview too.
We'll see.