Magento 2 Debugging

Job ID: 35633648

Budget: €12 – €18 EUR

I run a Magento 2.4.5 Shop (www.silentmodding.com) and suddenly, custom sorting in category item list (frontend) is not working any more. See example: https://www.silentmodding.com/en/gehause.html
Should sort by popularity value, but it does not anymore. When clicking on sorting direction, nothing happens.
Staging for developing shop exists.

The target of the assignment is to find the cause for the error and to support me in correcting it if needed.
Only 100% Magento 2 developers.

Any help would be appreciated!
Related categories: PHP Magento MySQL