If you are sending KFX files, you can set the cdetype to PDOC. One acquaintance is currently using a Python3 utility to set the cdetype to PDOC for his ebooks. Not sure if their method of placing the .py file on his Kindle PW4 in the /documents/eBooks and executing it after sending books to their Kindle from calibre is the best choice but it does seem to work for them. See
ebook_cdetype_to_pdoc on GitHub. Python version used is 3.13.1.
Edit: Forgot to mention that they keeps the book files in a single directory. If you use a directory structure, you would need to modify the python file to browse the subdirectory looking for books.