Windows – Prevent Xbox Game Bar popping up when opening applications

If you press Windows+G to go to the Game Bar, and open up Settings (the gear icon), you can uncheck "Remember this as a game", and it should make Windows not remember it as a game anymore.

Can this app or program exist outside of the UWP ecosystem?

The Game DVR feature and specifically the in-game Game Bar that appears in compatible applications, is controlled by the Xbox Universal Windows Platform application, which is one of the default provisioned UWP applications.

Is it a part of the Xbox app?

Yes

What method(s) are there to remove it?

In order to disable the Game DVR you have to disable it within the Xbox application.

How to Disable Game DVR (and the Game Bar)

Unlike most Windows 10 features, which can be configured in the Settings app, the Game DVR and Game Bar features are buried in the Xbox app.

1. Launch the Xbox app from your Start menu.
   • You’ll need sign in with a Microsoft account if you haven’t already.
2. Once you’re signed into the Xbox app, click the gear-shaped Settings button at the bottom-left corner of the app and then click “Game DVR”.
3. Disable the “Record game clips and take screenshots using Game DVR” option at the top of the screen. This will disable background recording, the Game Bar, and other Game DVR features.
4. Game DVR, including background recording and the Game Bar, will now remain disabled unless you return to the Xbox app and enable it.

Source: How to Disable Windows 10’s Game DVR (and Game Bar)

Is there a prophylactic to prevent such things in the future?

Once you disable the Game DVR functionality it will stay disabled.

How do I disable UAC on Windows 10 Home?

In order to turn UAC competely, open regedit, and navigate to following location.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System

You are going to have to modify the value of EnableLUA to 0. Setting the UAC setting to it's lowest setting, within the Control Panel on Windows 10, does not actually disable UAC.