I'm not sure how to fix this hum issue. Despite the large amount of noise reduction I apply, there's still a lot of hum.

As-is that’s better than most YouTube audio.

But, IMO, only 8/10.
I’m deducting points for excessive sibilance, (curable with de-essing),
and reverberation from the room, which can be reduced, (but not cured), with an expander like couture.
(Too much expansion will erode the speech: attenuating the start & ends of words).