After you get RMS Normalize, make sure your Mac didn’t “help you out” by renaming it. Right-click or Control-Click the file > Get INFO. That will tell you the actual name of the file and give you the opportunity to change it back. It’s not supposed to have .txt on the end.
Then, after you get that sorted, use Effect > Add/Remove plugins to make sure audacity can use it.
We publish an audiobook mastering process.
https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/1
It’s three steps and if you record in a quiet room, that could be all you need.
Koz