https://www.amazonforum.com/s/question/0D56Q000084mKpZSAU/what-will-happen-with-all-our-books-on-our-kindles-when-the-wifi-band-drops-the-3How to Transfer books to a Kindle via usb
go to the Amazon website
select Your Content and Devices from the upper right menu there
log in
find the book
click on the Actions button [...] in front of the title or the More button to the right of the title
Select transfer via usb and select the target device
then
Locate the file either on your desktop or within the file browser.
Connect the Kindle to your computer via USB cable.
Open File Explorer
Locate the “Documents” folder within the Kindle.
Drag and drop the PDF file from the original location to the Kindle “documents” folder.
Soooo after the fall (of 2 3G) you can still carry your old friend Kindle 1st 2nd Gen around with you by sideloading the eBooks of your choice from your Kindle account .. this is also an option from your computer, hook up your kindle and open files, drag and drop whatever eBooks you've downloaded .Starting this December 2021 , Mobile Network Operators (MNOs) in the U.S. will start phasing out their 2G and 3G networks (to learn more about MNO 2G and 3G network deprecation, click here). This means that some prior generation Kindle devices, including Kindle (1st and 2nd Generation) and Kindle DX (2nd Generation), will no longer be able to connect to the internet. Customers who own these devices will still be able to enjoy previously downloaded content on their Kindle, but they will no longer be able to access or download new content wirelessly.
Other devices, including Kindle Keyboard (3rd Generation), Kindle Touch (4th Generation), Kindle Paperwhite (5th Generation, 6th Generation, and 7th Generation), Kindle Voyage (7th Generation), and Kindle Oasis (8th Generation), will only be able to connect to the internet using Wi-Fi. If you are unsure which device you have, see Identify Your Kindle E-reader for more information.
You will still be able to download books and transfer them via usb.
But whatever you do, if your device is one of the three named in the first paragraph, do not reset them to Factory Defaults as you will not be able to register them again