1st Generation AirPort Express - Utility Issue
Background
I have a 1st-generation AirPort Extreme Base Station I bought in 2007 and am trying to sell it online. The last time I had used the Airport only two days ago to create a wireless network, but I have since gotten a combined Xfinity modem/wireless router that supplies my internet. For all these years, it worked perfectly and created a reliable WiFi network.
The Problem
Today, I performed a factory reset on the base station, and it has remained on the slow-blinking amber mode for a while. It is not appearing in my AirPort Utility app on my 2012 Mac running fully-updated MacOS Mojave 10.14. I tried resetting it again, and also tried hooking it up to my Xfinity modem/router (via ethernet WAN port), but it still isn't showing up as a new device under "Other Wi-Fi Devices."
Question
I found this article on The Mac Observer saying that Apple disbanded its wireless team in 2016 and will not longer be creating AirPort base stations. Since I had set this 2007 AirPort Extreme up with older (pre-Mojave) software, is the base station not showing up because Mojave has phased out their support for such an old model? What else could be causing the issue here, and is there anything I can do to make sure this base station is functional before selling it?
P.S. - I attempted a factory reset and connection via AirPort Utility with another 2012 (2nd-Generation) AirPort Express, and it connects perfectly, so there doesn't seem to be an issue with my Mac's connectivity or the AirPort Utility app.
Thank you! Any help is appreciated.
MacBook Pro, macOS Mojave (10.14), 2.6 GHz Intel Core i7; 8GB of RAM