Adding all your books to a single "Collection" allows you to trigger a bulk download from within the Kindle interface.
Click Deliver and select the Kindle device or app you want the books sent to. download all my kindle books at once
Amazon often limits selection to 200 items at a time . You may need to repeat this for each page of your library. Adding all your books to a single "Collection"
Downloading your entire Kindle library at once is a common goal for readers who want to back up their books or ensure they have access to their content offline. While Amazon's platform doesn't feature a single "Download All" button for an entire library, there are several effective workarounds to achieve a bulk download. You may need to repeat this for each page of your library
Go to the Manage Your Content and Devices page on Amazon.
In the Books tab, use the Select All checkbox at the top of the list.
The most official way to send multiple books to a specific device is through your Amazon account dashboard.