Windows 10: How can I bulk resize to 1:1 aspect ratio and add a black background to 4,000 images?

Hi,Windowws 11 operating system.I have over 4,000 images that have been taken using 3:4 aspect ratio and in many cases cropped to remove background or superfluous space.I'm trying to get all photos to a 1:1 square aspect ratio by having a black background and then putting the resized image on top of that background.I have power tools installed but this only allows me to resize the image to change the background and aspect ratio.Apologies, I've tried loading example images but each time I get a "failed to upload" error message.Hope someone can help :Chris

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Aspect ratios of images in the Windows 10 lock screen slideshow

So the Windows 10 lock screen slideshow has limitations on the aspect ratio of images it displays. It prefers landscape images over portrait, but can not display panorama (like 4:1 aspect ratio).

 

Aspect ratio adjustment

The aspect ratio of my screen is wrong. The picture is all stretched out with black on the top and bottom of the desktop background. How do I get the ratio back to normal?

 

Change monitor aspect ratio

The aspect ratio of your monitor is fixed and can't be changed, because it depends on the arrangement of the pixels on the screen.

When you display an image on your monitor whose aspect ratio is different from the aspect ratio of your monitor, what you'll see depends on how different the aspect ratios are. Usually, you see black bars on the top and the bottom of the screen, or on the
left and the right, a familiar appearance known as 'letterboxing.'