ModifyTcaSelectFieldItemsEvent 

When it is dispatched 

The item provider of the field dispatches the event once each time the items of the field are built, after it added its own items. In the backend that is each time the record or the content element is opened in the form. The parameters a listener hands back are what the field offers.

The job form of academic_jobs builds the options of its two selects in the frontend from the same item providers, so the event is dispatched there as well, and an item a listener removes is neither offered in the backend nor in the form.

What a listener reads and changes 

The parameters are those of an itemsProcFunc , see the TCA reference. The keys a listener needs most:

In the backend form, TYPO3 hands the items it built before the item provider runs, the static items of the field and those of a foreign_table, as \TYPO3\CMS\Core\Schema\Struct\SelectItem objects, on TYPO3 v13 and v14 alike. The items a provider adds are arrays, and the job form of the frontend hands every item over as an array. A SelectItem implements \ArrayAccess , so a closure typed array|SelectItem that reads $item['value'] works for both.

An item is therefore not always an array. A closure typed array alone raises a \TypeError in the backend form for a field with static items.

The event declares these parameters once, as the PHPStan type alias ItemsProcFuncParameters , and the item providers import it. A listener or an item provider of a project imports it the same way, so static analysis checks it against the values above:

/**
 * @phpstan-import-type ItemsProcFuncParameters from \FGTCLB\AcademicBase\Event\ModifyTcaSelectFieldItemsEvent
 */
final class MyItemsProcFunc
{
    /**
     * @param ItemsProcFuncParameters $parameters
     */
    public function itemsProcFunc(array &$parameters): void {}
}

Example 

A site does not offer theses on its job board and never shows the room of a person. One listener removes both items. It checks the table and the field first, because it is called for every field of the table above:

<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\EventListener;

use FGTCLB\AcademicBase\Event\ModifyTcaSelectFieldItemsEvent;
use TYPO3\CMS\Core\Attribute\AsEventListener;
use TYPO3\CMS\Core\Schema\Struct\SelectItem;

final readonly class RemoveUnusedSelectItems
{
    /**
     * The values to remove, by table and field.
     */
    private const REMOVED_VALUES = [
        'tx_academicjobs_domain_model_job' => [
            'type' => ['3'],
        ],
        'tt_content' => [
            'settings.showFields' => ['contracts.room'],
        ],
    ];

    #[AsEventListener(identifier: 'my-extension/remove-unused-select-items')]
    public function __invoke(ModifyTcaSelectFieldItemsEvent $event): void
    {
        $parameters = $event->getParameters();
        $removedValues = self::REMOVED_VALUES[$parameters['table']][$parameters['field']] ?? [];
        if ($removedValues === []) {
            return;
        }
        $parameters['items'] = array_values(array_filter(
            $parameters['items'],
            static fn(array|SelectItem $item): bool => !in_array((string)($item['value'] ?? ''), $removedValues, true),
        ));
        $event->setParameters($parameters);
    }
}

The value is compared as a string, because the item providers declare some values as integers and the backend hands others over as strings.

Rules and pitfalls 

• Check table and field. One listener is called for every field of the table above. A listener that does not check both changes all of them.
• No record in the frontend. In the job form, the parameters carry items, config, TSconfig, table, row, field, effectivePid and site, and none of the keys of an inline parent. row is an empty array there, because the job does not exist yet. The event declares row optional, so static analysis reports a listener that reads it without a fallback. Read it as $parameters['row'] ?? [] , and every field of it with a fallback too, as $row['pid'] ?? $parameters['effectivePid'] .
• The inline uids are not always integers. A listener that passes $parameters['inlineParentUid'] to a parameter typed int raises a \TypeError for every record that is not edited as an inline child, because the value is '' there. Cast it first.
• A FlexForm field has two rows. row holds the values of the FlexForm, the content element is flexParentDatabaseRow.
• Keep the stored values in mind. Removing an item hides it from the form, it does not change the records that store it already. A single select shows such a value as an invalid value. A multiple select, such as Show only selected Fields, no longer shows it, and the next save of the record drops it.
• Keep the list a list. Pass the items back with consecutive keys, with array_values() after a filter, so the order is the one the backend shows.
• No order is promised between several listeners. A listener that has to run after another one says so with the after argument of #[AsEventListener] .

Introduced in 

The event exists since version 2.1. The extensions that dispatch it describe in their own changelogs when they started to, for example academic_jobs 2.1 and academic_persons 2.4.