Amazon posted a new Help Page for Kindle for Mac:
https://www.amazon.com/kindle-dbs/arp/B0C9PRPV28
It's strange and interesting that the new Kindle for Mac is an Intel app when the beta was Silicon. But that's good news for owners of older Macs. You do need macOS 11 (Big Sur) or higher.
Support for the old Kindle for Mac (now called Kindle Classic) is now ending "by Oct 31" (previously they just said "by October").
Kindle for Mac 1.40.1 can no longer be downloaded from Amazon's website. When you click on the
Download for PC & Mac button, it redirects you to the Mac App Store.
We'll see if "no longer supported" means 1.40.1 stops working altogether, or it just won't receive further updates