Listening with my ears now (the best way, I found). You have a pronounced sibilance and are hitting your S sounds hard. I applied DeEsser at these settings and it tamed the crispness. The tool is sensitive to volume, so do it after mastering. https://wiki.audacityteam.org/wiki/Audiobook_Mastering ht...
I'm working in the field right his second, so I can't listen, but I didn't have any trouble mastering your work to ACX Audiobook Technical Compliance. I pushed modest noise reduction in there just to be sure. Again, I can't tell what you or your background sounds like. I'll do that a bit later. But ...
So you use Skype or other chat or conference app? Do you leave it running in the background when you record? Those can do it, too. Restart the machine and only start Audacity. That appears to be chat auto noise reduction or environment suppression. Windows, odd system setups or chat apps can all do ...
That 6dB drop (half) between stereo and mono waves may be normal in your system. That's the system "making room" for the addition of left and right to make mono. The bottom trace in your illustration is almost normal. Push the volume control all the way up on the 2i2, record in stereo and ...
There is a desperation method of boosting microphone volume with the application of a Cloud Lifter between the microphone and the interface or mixer. You won't be doing that because the Lifter "uses up" the 48 volt phantom power leaving nothing for NT1-A. So this has to work with no tricks...
OK, this may take some time. Scarlett 2i2 Gen-3 has "modes," and you have to understand what they are and how to use them. Apparently, it "marries" itself to the computer and the Scarlett software and registration system. I have no idea what the "AIR" setting does and n...