• GL DDNS: hj82918.glddns.com (obfuscated)
  • Opal (GL-SFT1200): LAN IP 192.168.18.1, Role: WG Server
  • Slate AX (GL-ATX1800): LAN IP unknown, WAN IP unknown, Role: WG Client

Based on the result of your last nmap probe for your ddns it appears your Slate AX is connected to your ATT modem. Is this the case?

If so which device do you intend to act as the WG Server? The Opal or Slate AX? The Opal, correct? If so that should be the one connected as ATT ISP → Opal WAN.