I have been trying to fix a file for an audio book that keeps giving me the same problem.
It seems that the tracks are louder than -3db and that the RMS levels are also incorrect, above 23 decibels.
Every time I fix the db level the RMS level gets out of range (above 23decibels). Every time I fix the RMS levels the db get louder than -3db. Did anyone here faced the same situation?
If the peak level is too high when RMS is at the right level, you may need to apply some compression. That will gently “squash” the highest peaks down to an acceptable level. See Audiobook Mastering - Audacity Support for a guide on that.
FYI - Linear volume adjustments make the same change to EVERYTHING. If you reduce the level by 3dB, the peaks, RMS, and noise level all go down by 3dB. (3dB more negative.)
Limiting (and other compression) is non-linear. You can “push down” the peaks with very little-or-no effect on RMS, and zero effect on noise.