This is an overview from a recent similar post.
https://forum.audacityteam.org/t/trying-to-get-things-right-for-acx-submission/38743/19
It’s written for Audible/ACX, but the problems and solutions are similar.
The three tools in Mastering should be taken in order as they depend on, and clean up after each other. Don’t add any tools or leave any out.
Mastering is handy even if you’re not reading for audiobooks as the resulting voice files can be successfully submitted almost anywhere else.
As mentioned in that post, nobody does theatrical evaluation any more, so there’s no way to tell ahead of time that your speaking style is unacceptable until after you read the whole book, submit, and fail.
Do post a voice sample here when you get that far.
https://www.kozco.com/tech/audacity/TestClip/Record_A_Clip.html
Koz