PC connecting to WiFi but no IP address assigned

My gateway/router was updated to a XB8 (CGM4981COM) to address an Xfinity stream app issue on my TVs.

All of the devices on my network work just fine, except one.   That one device is an older PC (but upgraded to Windows 11) that is connecting to my WiFi network but shows a status of 'No internet'.  Running IPCONFIG shows that it is being assigned a default Windows IP address and subnet mask.  Running IPCONFIG /renew just hangs.  Assigning an IP address manually does not help.

The Windows settings show that it is connecting to the 2.4 GHz network using the 802.11n protocol.  The adapter isn't responding to attempts to force it connect to the 5 GHz network.  I don't see any settings that would allow me to force using either the b or g protocols. Although the adapter documentation states that it supports both.   The Xfinity Gateway 'EDIT 2.4 GHz' page shows that the Channel Mode is set to g/n/ax.  On my previous router this was set to b/g/n.  The control is DISABLED because it is "being managed automatically to help optimize [my] home network" and these settings are no longer available in the Xfinity App.  So, I don't even get to try that as a solution.

Discussions with Xfinity technical support have been frustrating at best.

Any ideas on how to deal with this before I invest in some new hardware?  If I do what would be better (more likely to fix the problem) a WiFi extender, access point or a new adapter?