Device frames images from Apple website too large and greyed out

I am creating the images for my app to be published on the App Store.
I have images depicting the use of my app with sizes corresponding to what is requested, as this page reads:
Screenshot specifications - App Store Connect Help (apple.com)
Now I want to use also the device frames that can be found at:
Marketing Resources and Identity Guidelines - App Store - Apple Developer
putting the screenshots inside the frame with just some adjustments.
Example:
I downloaded the iPad Pro 12.9 frame image but it is way too large if compared with the screenshot.
I opened it in Gimp and it is much larger then expected.
Moreover it is greyed out, and also when I paste the conteng image it is greyed out.
This is the first time I am releasing an app with Apple so this question could be silly.
Still I need help.
Other questions of mine went unanswered. I hope this one will have some answers.
Thank you

Device frames images from Apple website too large and greyed out
 
 
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