I'm not much a collector of audiobooks, but I found Intag very interesting, thanks. There's some documentation here:
https://github.com/Jamminroot/intag. I wish i had read this remark on Softpedia before installing it:
Despite the app’s quick setup experience, users need to bear in mind that the executable needs to be placed in a dedicated program folder on first boot, since its context menu trigger will look for it in its initial location.
On first use I added test tags to some windows folder, then I searched for tags:test, and it worked fine on Windows 10. There's also some insteresting information here on tagging files on Windows:
https://www.makeuseof.com/windows-11-search-tags/
Have you tried foobar? I use the latest 32 bit preview version just for music, but some folks like to use it for audiobooks:
https://www.reddit.com/r/foobar2000/...to_audiobooks/
(i have this
component installed, and if it weren't for its existence, I would still be using winamp nowadays, as it's been recently revived)