Can't open Outpost Firewall Pro settings; blank dialog boxes with no text after Windows 11 upgrade

I've only just upgraded to Windows 11 and it's already a disaster right out of the gate. I'm running Outpost Firewall Pro 9.3 (4934.708.2079), which I'm fairly sure was the last version released. It's an antique piece of software that was bought up by a competitor many years ago and then promptly killed off. Paying for another firewall is out of the question, and the last time I had a look at the free ones, they were garbage.

With that preamble out of the way, here's the actual issue that I'd greatly appreciate help with:

• There's no way to open the Advanced Settings window. Both systray icon menu - Advanced Settings and Settings window - Settings - Advanced Settings don't do anything. Settings window - Firewall - double-clicking on a program does nothing (it's supposed to open its rules window). Repeating this last action a few times crashes the program (the window and systray icon silently vanish).
• My first thought was to reinstall the firewall. Trying to do so brings up a blank dialog box. Answering either Yes or No makes no difference; nothing happens.
• The firewall's notification popups also appear to be blank, though that's the least of my worries right now.
• I thought my custom DPI/scaling might be an issue — though it wasn't in Windows 10 — but there's no difference after resetting to the default value and logging out.
• I already have the latest graphics driver.
• I ran sfc /scannow which has never solved any problem and unsurprisingly that's the case again here. It didn't find any integrity violations.

Try running the firewall software in compatibility mode. Right-click on the executable, select 'Properties', go to the 'Compatibility' tab, and check 'Run this program in compatibility mode for:' then select 'Windows 10'. This might help if the issues are related to the software not being able to interface with the new Windows 11 environment properly. If this doesn't work then you are likely going to have to use something else. Windows Defender Firewall is quite robust and has been significantly improved over the years.

There's no Windows 10 setting for compatibility mode. It only goes up to Windows 8. I tried setting that for all users, restarted the system, no dice.

The uninstall application doesn't work either. Trying to rip out the firewall piece by piece has proven difficult:

I have Agnitum Firewall Driver stuck in my network adapter properties. It won't let me remove it with the Uninstall button because it's required by Agnitum Firewall.

I went on a cleaning spree in the registry, but it won't let me delete the following key, even in Windows Safe Mode. It won't let me change permissions for the key either.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center\Provider\Fw\{BFD97B08-B281-A36A-4414-803D4491AB1D}

The only other two things I can suggest are either, first try to restore your system, to a point when everything was working to your liking, or if you can't re-install, you may have to do a complete reinstall.

UPDATE:

there are a few third party un-installers you can can try. Maybe they will be able to un-install Outpost Firewall.

The driver remains stuck in the network adapter properties. I used DriverStoreExplorer to remove it from the Windows driver store, though it didn't seem to change anything.

I found directions on SuperUser to take ownership of the aforementioned registry key and managed to delete it. I believe the only trace remaining in the registry now is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center\ProvidersMigration\WicaAvDisplayNames - string entry "0" with the value "Outpost Firewall Pro" which I'm not sure is worth messing with permissions to remove.

As an aside, the Portmaster seems like a pretty nice, free, full featured firewall so far. TinyWall and simplewall were others I looked at that seem like fine choices as well.