This snippet with check a specific checkbox field in a specific form to see if all choices have been selected, if it they are the entry will be marked as spam.

check-all-mark-as-spam.php

<?php
//Copy everything below this line

/**
*
* Mark entry as spam if all checkbox choices are selected
*
* This is a unique use case, but if you have a checkbox that selecting all choices is unlikely you can use this as a spam prevention method.
*
*
* @Version: 1.0
* @Author:  Chris Eggleston
* @license: GPL-2.0+
* @link:    
*
*/


//replace 1 in gform_entry_is_spam_1 with your forms ID number
add_filter( 'gform_entry_is_spam_1', function ( $is_spam, $form, $entry ) {
    $checkbox_field_id = '1'; // Replace 1 with your checkbox field ID

    // Attempting to accurately count the selected checkboxes
    $field = GFFormsModel::get_field( $form, $checkbox_field_id );
    if ( ! $field instanceof GF_Field_Checkbox ) {
        return $is_spam; // Ensure this is a checkbox field
    }

    // Initialize count
    $selected_count = 0;

    // Loop through all inputs (checkboxes) of the field and count the ones that have a value
    foreach ( $field->inputs as $input ) {
        $input_id = (string) $input['id']; // Cast to string to match array keys
        if ( ! empty( $entry[ $input_id ] ) ) {
            $selected_count++;
        }
    }

    $total_choices = count( $field->choices );

    return $is_spam;
}, 10, 3 );