Logo-proportion

On page https://yoast.com/social-media-optimization-with-yoast-seo/ it says: ‘Then, set a good default image under the site basics settings. This image is used when you have a post or page that does not contain an image. […] Facebook is forgiving when uploading images, but 1200px by 630px should work well.’

I have now designed my logo in the format 1200px (height) by 630px (width) and replaced the standard square image (with the mountain landscape) on the Yoast backend page under General -> Website Appearance -> Organisation with my logo.
However, the preview now shows a centred square section, which looks rather unflattering.
So: Is it correct to design the logo as a long rectangle or as a square rectangle? (It should be used on Pinterest.)
Thank you and kind regards

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The page I need help with: [log in to see the link]