Calibre after version 6.0 (and any version after 11th of July 2022) has a Full Text search internally implemented
Full Text search
Then, enable indexing for the current library. Once indexing is complete you can search all the text in the full library. When you add new books to the library, they will be automatically indexed in the background. This search allows you to quickly find all books that contain a word or combination of words. You can even search for words that occur near other words, as shown in the examples in the search popup window.
calibre can optionally index the full text of books in the library to
allow for instant searching of words inside any book. To use this
functionality click the FT button at the left edge of the search bar.
This button takes you to the full text search:
More on how to use the search in the manual:
https://manual.calibre-ebook.com/gui.html#searching-the-full-text-of-all-books