Try configuring the PlayMaker WebGL dll to use with Xbox Game Core:
https://docs.unity3d.com/Manual/PluginInspector.htmlThe WebGL dll excludes Unity libraries that are most commonly not supported on consoles. For example, it's used to publish to Switch, Playstation, XBoxOne etc.
There might also be individual actions that need to be defined out. For example, you will see some actions with UNITY_SWITCH || UNITY_PS3 || UNITY_PS4 || UNITY_XBOXONE defines. I'm not sure what the XBox Game Core define symbol is (we don't currently have a devkit). I'll try to find out, or if you know what it is, please let me know!