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please increase that image width to 1140, and try to reupload it.
I check directly:
https://[your site domain]/components/com_community/assets/frontpage-image.jpg
the image quality still low. make sure when you convert it to JPG, that image quality still using 100%. if still blurry. please send that image to This email address is being protected from spambots. You need JavaScript enabled to view it.
or try to upload it manually to
https://[your site domain]/components/com_community/assets/frontpage-image.jpg