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If you have received an email from Google Search Console indicating new mobile usability issues, it means that your website is not mobile-friendly, which can negatively affect your search engine rankings and overall user experience. To fix these issues, you can start by checking your website on mobile devices to see how it appears and what changes need to be made.
For the specific issues mentioned - Text too small to read, Clickable elements too close together, and Content wider than the screen - you may need to increase your website's font size, spacing, and layout to ensure that they are mobile-friendly.
For the viewport not set issue, you may need to add a meta tag to your website's HTML code to ensure that it scales properly on mobile devices.
For 'Content wider than screen', Modify the width and set media queries in your CSS file.
If you are not familiar with web development, it may be best to consult with your developers or a web development agency to help you fix these issues. Alternatively, if your website is built on Magento, you can check if there are any mobile-friendly themes or extensions available that can help you solve these problems.