Windows 10: Custom file extension not working on Windows 10

I added a custom file extension (".custom" for example) to HKEY_LOCAL_MACHINE\SOFTWARE\Classes, and set its value to "batfile", so it would run as a batch file. This works fine on all my machines, except the one running Windows 10. I get an error: "This app can't run on your PC", when I try to run anything with my custom extension ("file.custom" for example). The solutions online say to disable Windows SmartScreen or enable App Side-loading in the settings, but I do not have a Windows SmartScreen option available and App Side-loading is already enabled. One solution said that if you don't have the Windows SmartScreen option in Settings, then disable it in Windows Defender, but my Windows Defender is already disabled.
I tried changing it's value to "txtfile" and it worked, but I couldn't change it back. Now, any time I make a new file extension, they all open as a text file regardless of what their value is. I've tried restarting the computer. I don't understand what is going on. Can anyone help me solve this issue?

:)

 

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**Moved from: (Windows / Windows 10 / Windows settings).**

 

Just considering Smart Screen:

You should consider whether disabling a protective element of the OS is worth it.
How to Disable the SmartScreen Filter In Windows 8 or 10

If you have Win 10 Pro up, you could use group policy.
Available Windows Defender SmartScreen Group Policy and mobile device management (MDM) settings (Windows 10) | Microsoft Docs

http://www.askvg.com/tip-how-to-disa...in-windows-10/
mentions a reg edit.

You could also try accessing the Defender interface irrespective of whether Defender is disabled or not.

 

That's irrelevant, because I said I don't have a SmartScreen option at all to disable or enable.
Also, I can't access the Defender interface, because it's disabled.

 

Did you actually read what I posted for you?

A registry edit does NOT require Defender. Does it?

No, you launch... Defender? No. The registry editor.

If Windows is complaining about your custom stuff and Smart Screen, then surely smart screen issues are worth looking into.

Good luck. Bye.

 

The registry edit did nothing. When I launch Defender, it doesn't open, because it's disabled. I have no SmartScreen options to look at.