How to bulk delete books from Apple Books?
This is not a question, but rather a response to multiple users asking the same question over the years with really no adequate answers being given. The best way to bulk manage the books in Apple Books is within the folder where they are stored via:
System Settings > Apple ID > iCloud > Account Storage > Manage... > Apple Books > Show in Finder...
In Finder is a list of books in a folder called 'Books'.
The pic below depicts the path using the Path Finder app which allows me to dig through folders unimpeded unlike the Mac OS Finder which tends to obfuscate.