Hello @Filip,
Thank you for sharing the details of your tests. We appreciate your efforts, and it appears that we were aligned in our observations.
The primary cause of the performance slowdown is related to the WooCommerce cart fragments script. You can find similar reports and discussions on this issue in the official WooCommerce GitHub repository: https://github.com/woocommerce/woocommerce/issues/31981.
As for your current setup, there are two possible solutions:
1. You may disable the off-canvas content, as you have already discovered in the Cart Widget settings.
2. Alternatively, if the cart fragments script is active, you can disable it via Theme Options → Speed Optimization.
Additionally, we recommend reviewing the following article, which provides further insights into the use and impact of the cart fragments script: https://www.businessbloomer.com/woocommerce-why-how-to-disable-ajax-cart-fragments/.
Please note that we are currently experiencing a high volume of support requests. However, our development team is actively working on performance improvements, and the test results you have provided are valuable in helping us enhance our theme.
Thank you once again for your input and understanding.
Best regards,
Jack Richardson
The 8Theme Team