sure re 1) had same concern, kvrt NPE report clean, 2) cmd sfc, netsh, windows firewall diagnostic tool... all failed to start WF Service error code 0x6d9 before I installed CF. I do not "love" CF, but liked it in the past, and since I'm on win10, not sure CF 2 yr old issue is problem here. & CS says it's working. I do see this situation as somewhat temporary. I see new hardware foreseeable future... Appreciate your feedback.
Did you try a System Restore point? If you have one, before Windows Firewall stopped, then it'll be worth trying it. Or if you have an Image, also it might work.
Did you google "windows firewall 0x6d9 error"? You'll see lot of possible solutions:
It seems that sometimes the 0x6d9 error appears because other services (needed for Windows Firewall) are stopped (for example "Base Filtering Engine" etc). Please, restore Windows services default status.
In other cases, it seems that resetting permissions for Microsoft Protection might solve the issue:
HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Services \ SharedAccess \ Epoch
HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Services \ SharedAccess \ Defaults \ FirewallPolicy
HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Services \ SharedAccess \ Parameters \ FirewallPolicy
At every key, right-click (Default), choose Modify and input the value data: NT SERVICE \ mpssvc.
In other cases, it seems that resetting Windows Firewall default settings might fix the 0x6d9 error:
netsh advfirewall reset
net start mpsdrv
net start mpssvc
net start bfe
regsvr32 firewallapi.dll
Please, google the subject (0x6d9 error), and you'll find more possible solutions.
If nothing works for you, then you might try "Windows Refresh" (it'll reinstall your Windows, your apps are going to be removed, but your personal stuff will be kept).
Another solution is to make an Image of your current Windows 10, upgrade to Windows 11, almost sure this will solve your Windows Firewall problem... and then downgrade to Windows 10.
In short, it seems you have lot of alternatives. Good luck!
PS: With regards to current CF, sorry, all I can say is the same: You should never use a security software that is not updated/upgraded. It has nothing to do with your Windows 10 or Windows XP, 98, whatever. It's a matter of principle, there is no rational reason for using abandonware (and out-there you have lot of free firewall updated/upgraded). Also, you should not use abandonware just because one or million anonymous persons say that's "OK". You always must preserve your criticism. In real world, security software reputation is not built on "social media or anonymous characters/avatars in the web", you should trust only objective tests done by well known third-parties, or well known (not anonymous) experts.