First, only one firewall will run at a given time, not both so not sure where you are getting the idea that two firewalls are running at the same time as it is not even possible. Even Windows will show that the Windows Defender Firewall is disabled and only using Norton Security with Backup as the active Firewall. Where does it say that FirewallMonitor plug-in is only for the Windows Defender Firewall? Ofcourse, if it only supports Windows Defender Firewall and not third party firewalls, then the problem is easily solved by not using it even though I think instead of PH getting killed with the FirewallMonitor plug-in, it should instead just autodisable itself so PH will run without it. So there i no Norton Smart Firewall and Windows Firewall at the same time as Windows will not allow it as seen in the screenshots below. Once you use any other firewall, it usually will register itself and Windows Defender Firewall is automatically disabled. When there are no other firewall running or the other firewall is disabled, then Windows Defender Firewall will automatically be enabled and active as the current firewall. There is no need to uninstall Norton Smart Firewall to solve the current problem either as all one needs to do is disable the Norton Smart Firewall in Norton Security with Backup permanently or until system restart as seen here:
Windows will only allow one firewall to run at a given time so this will happen:
1) Norton Security with Backup runs with Norton Smart Firewall, Windows 10 Firewall aka Windows Defender Firewall is automatically disabled.
2) Norton Smart Firewall is disabled, Windows 10 Firewall aka Windows Defender Firewall is automatically enabled
What you are saying is Norton Security with Backup runs with Norton Smart Firewall active and Windows 10 Firewall aka Windows Defender Firewall is also active, that may be possible but not in this case as only one firewall is active. See below as this is confirmed by Windows that shows Norton Security with Backup as the active firewall and Windows Defender Firewall as inactive:
Even in this page, you can't turn on or off Windows Defender Firewall because those options are not even clickable as Windows already says Norton Security with Backup is handling it which means Windows Defender's Firewall is already disabled:
So in response to what you said:
Then you cannot solve your problem. - problem is easily solved, see above. If FirewallMonitorPlugin.dll cannot run with any firewall other than Windows Defender Firewall, then just don't use it.
Norton Smart Firewall and Windows firewall at the same time they can not go, - See above, Norton Security with Backup is the active firewall, Windows Firewall is inactive so they are not running at the same time.
Norton Smart Firewall automatically and fully take control of the built in Windows 10 Firewall. - That is incorrect as Norton Smart Firewall runs, Windows 10 Firewall automatically is inactive. They will never run on the same time unless the third party firewall does not register itself as a firewall.
I'm sorry but you will have to decide for only one. - It is only running one, it will never run both in my case atleast. If you have Norton running, Windows Firewall will not run. If you don't have Norton running, Windows Firewall will automatically activate. I am sure there are people who actually run two firewalls at the same time but not in this case.