Hello,

You can create a preset with the condition that is related to product pages in Theme Settings -> Settings Presets -> create such condition: https://take.ms/6wAhW , then edit that preset and in General -> Layout set the custom width: https://take.ms/243Zh

Here is our documentation on how to use presets: https://xtemos.com/docs-topic/theme-settings-presets/

Kind Regards