Hey y'all! I'm the person who created the Reddit thread and I wanted to come and add a +1 to this thread as well.

I want to emphasize that especially after reading user Packetdancer's take, I'm 100% sure this issue is exclusive to Final Fantasy XIV in the way they described it:

Quote Originally Posted by Packetdancer View Post
Anyway, it's worth noting that the Series X controller does not have the same button mappings at a HID report level. If a game is using XInput (i.e., Divinity 2), then the Series X controller should show up fine because Microsoft does provide an XInput driver for it. If a game is trying to access gamepads directly as HID devices in order to use extended features, then they'll need to add custom mappings for the Series X controller for it to work correctly.

My gut feeling here, not having dissected FFXIV's input functionality, is that for USB gamepads it just uses it as an XInput device, thus letting Windows map the HID reports to sane, recognizable XInput values. However, I'm guessing that with wireless controllers it iterates through them to try to recognize them individually, so that it can spot a PS4 DualSense controller (which doesn't function wired on Windows, so will only ever be wireless) and use their own custom code. But as the Series X controller has a whole new product identifier, FFXIV probably has no idea what to do with it, so doesn't use it with XInput and instead reports it—admittedly accurately—as an unknown controller with 6 axes and 16 buttons.

So, unfortunately, likely the best approach here is either "wait until SquareEnix makes FFXIV recognize the new device, and either has mappings for it or handles it as an XINput device" or else "use a program that lets you remap buttons such that you can make the buttons be what FFXIV expects from a generic gamepad in the meantime."
Dynratygus, as much as I appreciate the support you are able to give, I was told by Square Enix Support to come to these forums to report this issue. I would like to know whether or not this issue is going to be able to get rolled up to a higher channel that can hopefully affect change with the way the game recognizes our controllers. Playing wired is not ideal whatsoever when my controller works perfectly via Bluetooth on every other game I play on my PC. :-(