I found this amazing program called "Fakin’ The Funk" that I use alongside MusicBee to keep my library in check. You might think your library is all at 320 bitrate but it's probably not.
About half of all MP3s in the wild are fake or upscaled by people who have no clue how lossy file compression works (https://www.digitaldjtips.com/2017/01/your-questions-converting-mp3s-from-128kbps-to-320kbps/).
I've even had MP3s I bought from the top companies that were not the bitrate they were supposed to be. It's rare but it happens.
Fakin’ The Funk will allow you to import your entire loss and lossless audio collection (supported audio formats at this time are MP3, MP4/M4A, OGG, OPUS, FLAC, WMA, AAC, ALAC, MPC, SPX, SFX, TTA and WAV) and batch scan them to calculate and display bitrate and frequency. If the scan finds a wrong bitrate or lower peak-frequency, Fakin’ The Funk will show you the audio files actual bitrate.
Another nice feature is that Fakin’ The Funk can also detect upscaled files. So if an MP3 has been upscaled from say 128kbps to 320kbps, it will tell you that after you batch analyze.
After all your audio files have been analyzed you have the opportunity to then rename the lower-quality files, copy, move or send them to the recycle bin.
(https://d2.alternativeto.net/dist/s/fakin-the-funk-_659659_full.png?format=jpg&width=1600&height=1600&mode=min&upscale=false)
It also has a very nice spectrum analyzer and you can save them as images.
(https://fakinthefunk.net/assets/FTF-running-on-Ubuntu-POL-1.png)
You can find it here and it's $20 or €15.99:
https://fakinthefunk.net/en/
DISCLAIMER: I am not affiliated in any way with the program or it's authors, and I'm not being paid (I wish) for this post.
If you want something not quite as automated but free and cross-platform, check out Spek:
http://spek.cc/
(P.S. This would be a super cool feature for MusicBee)