I wrote a process for this incorporating some custom tools, one of which is the ability to set RMS directly instead of running around the bush. Audacity 2.1.3 or later is required.
https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/1
As a fuzzy rule, this is not a menu that you pick and choose. The tools depend on one another to work and you should not leave any out.
The process will get you 2/3 of the way there instantly with the only variable being noise. Noise is its own posting. It’s not fun.
Koz