Warning: Illegal string offset 'pk_i_id' in /home/pakhomec/public_html/oc-content/themes/wizestate/search-sidebar.php on line 5

Warning: Cannot assign an empty string to a string offset in /home/pakhomec/public_html/oc-content/themes/wizestate/search-sidebar.php on line 5

@abuzarkandwal
You are trying to get key 'pk_i_id' on string instead of array.
Pretty common notice.

please explain in simple worrds

Check i.e. stack overflow.
https://stackoverflow.com/questions/52478186/how-to-fix-this-illegal-string-offset-error-in-php

try this

$category = osc_category(); // Retrieve the current category as an array
    if (!isset($category['pk_i_id'])) {
        $category['pk_i_id'] = null;
    }