Problem with setting the default value for a ManyToOne relation but only when used in livecomponent with livecollection

[gewait]

I have an entity "Main" which has a OneToMany relation named "children" to the entity "Child".

class Main
{
    #[ORM\OneToMany(targetEntity: Child::class, mappedBy: 'main')]
    private Collection $children;

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Inside the "Child" there is a ManyToOne relation named "other" to another entity named "Related".

class Child
{
    #[ORM\ManyToOne]
    private ?Related $other = null;

---

When a new child is created I want to set a default value for the relation "other".

I can't do it in the constructor of the entity because I would need the entitymanager for that.

I can't use a factory class, because I want to use this in a livecomponent with a livecollection
and there the creation of the objects is done internally.

So I do it via the data option in the formtype for child:

    src/Form/ChildType.php

    $builder
        ->add('other', EntityType::class, [
            'required' => false,
            'class' => Related::class,
            'choice_label' => 'name',
            'data' => $this->relatedRepository->findOneByName('when_this_is_preselected_then_it_works'),  //set default
        ])

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This does work in a normal form

but does not work in a live component with a live collection.

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Since the live collection does all the work internally when creating/adding a new child,
I don't know how or where I can initialize the child.other relation property!

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Is this the expected behaviour? What am I doing wrong? Can someone help?

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Reproducer:

live-collection-reproducer-zip.zip