Form field for media gallery does not appear when its render in a collection of forms

[pluscom-maxime]

Symfony version : 5.3.2
I have an entity Project which can have sevreal Steps, in my projectTypeBuilder i have this field (the collection of Steps)
->add('steps', CollectionType::class, [ 'entry_type' => StepType::class, 'entry_options' => [ 'label' => false, ], 'by_reference' => false, 'allow_add' => true, 'allow_delete' => true, ])
And in my stepFormType i have the Artgris media gallery field :
->add('gallery', MediaCollectionType::class, [ 'conf' => 'default', ])
When i add a new step from a project, the form gallery field won't appear until i save the step without gallery field..