Orbi: Can't upgrade firmware on RBR40 / Can't load config from another RBR40

Have an existing RBR40 that is 3+ years old, and has started occasionally rebooting itself, so I purchased a replacement RBR40.  This thread is NOT about why my old RBR40 is rebooting, it is about trying to use configure a new replacement.

I backed up config from the old RBR40 (running V2.7.3.22) to a file, and when I try to upload to the new RBR40 (running V1.8.0.4) I receive error: "Please select correct configuration file".

So the problem might be that the differences in firmware between old and new are too great?

But when I check for updates online on the new RBR40, I see V1.8.0.4 is running, but it says "No new firmware version available" when I click the [Check] button.  Very weird.

So I downloaded the latest RBR40 firmware from the Netgear web site (RBR40-V2.7.3.22.img), and when I try to upload it to the new RBR40 I receive error: "The firmware is incorrect ...".

Any ideas why this new RBR40 might be stuck in the past?