@David-TP Thank you for the response. I've come to realize I referred to the wrong model in my initial post, I actually have the Deco M9 Plus. That being said, I did state the correct firmware I currently have, the 1.2.12, so it is out of date.
I've looked over the links you've provided, but ran into some issues. The Deco app says I have the latest firmware, but as we've established that isn't true, so I can't use that method to update. I haven't been able use the web interface to update/get the latest firmware either, as I have tried to go to the webpage and the page never loads, as I keep getting "DNS_PROBE_FINISHED_NXDOMAIN" error. I have even tried the solutions on the "Fail to log into the web management page of Deco" that is on the FAQ, but was still unable to log into it, even when using the http://tplinkdeco.net:30000/ link.
I've tried using the Deco M9 Plus Update Assistant to update the firmware, since that's what it says to use for the M9 Plus, but it asks for a .bin file for the latest firmware. I click the link and select the M9 Plus model V2.8, but that just takes me back to the download page for the update assistant, so it's a cyclical loop.
So now I'm somewhat confused on how I can update the Deco M9 Plus to the latest firmware. Any more assistance or clarification in this matter would be greatly appreciated.