I've been looking for several hours, but haven't figured out how to expand simple (but not solid/monotone) backgrounds on Gimp.

Does someone have an article/tutorial/guide that they can link me? Or just someone who can give me some instructions?

Here is an example of an image backdrop where I would put this knowledge to use. This image is a cast promo image. In order to crop it down to the ideal aspect ratio (16:9) the image is destroyed (mostly because of having to chop the text in the bottom right in half). I would like to expand the area at the top and bottom of the image so that I can upload the backdrop (and other backdrops like this with a similar problem/situation). Here is a similar situation with an image poster (I only want to expand from the top in this scenario).

Additionally, it would be great to learn how to expand images like this that is a little more complicated- however, it still has a pattern-like background. EDIT: I tried doing on Gimp what this person is doing on Photoshop, but when I try to use the Stamp tool on Gimp after creating blank transparent space above and below my image (by increasing the canvas size's height dimension), the cloning doesn't apply to any of the transparent space and only clones onto the existing image.

EDIT: The above image can be cropped to the ideal aspect ratio, however I believe that changes the image significantly. It goes from an image with a brick patterned border across all four sides, to an image with no border/bar on it's left and right but a brick patterned bar at the top and bottom. It would be better if I wouldn't have to completely crop out the brick pattern on the left and right by expanding the top and bottom brick patterned bars instead.

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EDIT: ALTERNATIVELY, would it be appropriate to create a thread where I can give sources for image that require some image editing skills (that I clearly don't have right now) so that someone else can edit them and upload them?

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EDIT: Another user has suggested simply removing the backgrounds for these kinds of images and replacing it with a solid/monotone color. I'm assuming this isn't acceptable/encouraged for images?