Noise/feedback when listening back

If the “audio enhancement” is chopping-off everything above 8kHz before it gets to Audacity, then there’s nothing to work with above 8kHz.
An EQ change in Audacity cannot resurrect those frequencies if they have been removed.

That’s the noise-gate “audio enhancement”,
If a noise-gate is set correctly that can be avoided.
A good free plugin for inconspicuous gating is Couture.
(the free version is sufficient).

8kHz with conspicuous noise-reduction & noise-gating sounds like a Zoom/Skype call,
whereas 16kHz without conspicuous processing sounds like the person is in the room.

Your audiobook competitor$ are not restricted to 8kHz.