Hello @Eleni,
We regret to inform you that it is not possible to apply the size guide to the specific product category without using the single product builder. This would require extra customization at this time.
If you would like to change the behavior or add an option to enhance its functionality, please post your request on our taskboard at https://www.8theme.com/taskboard/. If it receives votes from other customers, our development team will attempt to include it in one of our upcoming updates.
Thank you for your understanding.
Best Regards,
8Theme’s Team