Hi @Rosabella Bojin,
Thank you for posting in this community.
I used my browser's developer tools to measure the title area of the image to be roughly 1865*228.
The official Share Point documentation does not specify the size of the image in the title area of the page. Microsoft recommends that images are landscape or 16:9 or greater in aspect ratio. You can try different combinations of image sizes with 16:9 aspect ratio. For example: 1280 x 720 or 1920 x 1080.
Reference: Image sizing and scaling in SharePoint modern pages.
We suggest that you can keep resizing your image until it meets your requirements based on the image sizes provided above.
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