Levelator working with Catalina?

Perhaps not the solution you're looking for, in that it is not free (the "Basic" plan is $6/mo), but Landr offers a great online tool to "Master" all audio, add levels, tone, warmth, etc. Hope some of this helps.

Amadeus is an audio editing software I've used for many years. They have a menu option Effects ==> Audio Units ==> AUDynamicsProcessor that does what Levelator did, and it takes only a few seconds instead of a few minutes to process the file. I run it through that effect twice and then Amplify the sound to my preferred level afterward. This is great for podcasting recordings where two people ended up at very different sound volumes in the file.

Check it out. It bills itself as the Swiss Army Knife of audio editing.

https://www.hairersoft.com/pro.html

The library Dynamic Audio Normalizer works with FFmpeg, you can install FFMpeg on macOS Catalina using Homebrew. Then to normalize the audio or video file run this command from the Terminal app:

$ ffmpeg -i <input_file> -af dynaudnorm <output_file>