If you bought them from Amazon, you won't be able to get them after the cutoff date directly to that Kindle via WiFi. You may not be able to get them in a format that old Kindles can read at all.

Download and back them up now. Or just pirate them if you need them later.

The entire Kindle store system will cease working on older Kindles after the cutoff. Still works as a reader, but expect to lose things like location sync across devices.

I don't buy from Amazon, I don't turn on WiFi on my Kindle because it eats battery life, I always travel with a laptop, and I only use it to read outdoors. So I really don't care. It's my beach book. At home, I'd rather read on my iPad.

Oh, and FWIW, you can install Tailscale to a jailbroken Kindle and Taildrop files to it over WiFi, if it can read the format (for the old ones being discussed, that's mobi or azw3).