System Restore Windows 10  

This is an additional method to perform a system restore after a system restore failure with stop error: 0xc000021a

Disable driver signature enforcement
How to Enable or Disable Driver Signature Enforcement in Windows 10

https://learn.microsoft.com/en-gb/wi...restore-points

Code:

Known issue: You cannot restore the system to a restore point after you install a Windows 10 update
Consider the following scenario:

You install Windows 10 on a clean computer.
You turn on system protection, and then create a system restore point that is named "R1."
You install one or more Windows 10 updates.
After the updates finish installing, you restore the system to the "R1" restore point.
In this scenario, the system is not restored to the "R1" restore point. Instead, the computer experiences
 a Stop error (0xc000021a). You restart the computer, but the system cannot return to the Windows desktop.

Cause
This is a known issue in Windows 10.

During the system restore process, Windows temporarily stages the restoration of files that are in use. 
It then saves the information in the registry. When the computer restarts, it completes the staged operation.

In this situation, Windows restores the catalog files and stages the driver (.sys) files to be restored 
when the computer restarts. However, when the computer restarts, Windows loads the existing drivers 
before it restores the later versions of the drivers. Because the driver versions do not match the versions 
of the restored catalog files, the restart process stops.

Code:

Workaround
To recover from the failed restart and continue the restore process

After the failure occurs, restart the computer until it enters the Windows Recovery Environment (WinRE). 
To do this, you may have to use a hardware restart switch, and you may have to restart multiple times.

In the Windows Recovery Environment:

Select Troubleshoot > Advanced options > More recovery options > Startup settings, and then select 
Restart now.
In the list of startup settings, select Disable driver signature enforcement.
 Note

You may have to use the F7 key to select this setting.

Let the startup process continue. When Windows restarts, the system restore process should resume 
and finish.
These steps restore the computer to its "R1" state.

To recover from the failed restart

To recover from the failed restart and roll back the restore process, follow these steps:

As described in the previous procedure, restart the computer and then enter WinRE.
In the Windows Recovery Environment, select Troubleshoot > Advanced options > System restore, 
and then select Undo system restore.
These steps return the computer to the state that it was in before you started the restore process.

To restore Windows to a restore point by using WinRE

To start the System Restore wizard on an affected computer, use WinRE instead of the Settings 
dialog box. 
To do this, follow these steps:

Select Start > Settings > Update & Security > Recovery.
Under Advanced options, select Restart now.
After WinRE starts, select Troubleshoot > Advanced options > System restore.
Enter your recovery key as it is shown on the screen, and then follow the instructions in the System 
Restore wizard.

This is a current Microsoft thread with the Windows 10 update, bugcheck 0xc000021a, and system restore failure:

https://answers.microsoft.com/en-us/...true#LastReply