Custom UniqueConstraint do not works with OneToOneField

[LECARROU]

I use many models with OneToOneField with default unique=True.

I would like the user to be able to create a record in table Exam even if one or more records are marked as soft (logically) deleted and linked to the same record in table Followup.
But when I have a model with OneToOneField, if I deleted a record 1 in table Exam linked to a record 1 in table Followup and I try to recreate a record 2 in table Exam linked to the same record 1 from table Followup, I get an IntegrityError because the uniqueness is not respected.

I read about the possibility of "revive" a deleted object but that's not what I want. I want to have multiple deleted records but only one undeleted one that respects the integrity of the constraints.
I read the section on field uniqueness in the documentation where a unique constraint can be set to exclude deleted records.
I try to implement this UniqueConstraint but it doesn't works.

I try to customize a ModelManager to set _safedelete_visibility = DELETED_VISIBLE_BY_PK but doesn't seems to works.
In my Postgresql database, a soft deleted object is not accessible with Exam.objects.filter(uuid='my-uuid') wherease it is for non soft deleted objects.

class Followup(SafeDeleteModel):
    _safedelete_policy = SOFT_DELETE_CASCADE
    uuid = models.UUIDField(default=uuid.uuid4, max_length=36, null=False, unique=True, primary_key=True)
    date = models.DateField("Date", null=True, blank=True)
    
class Exam(SafeDeleteModel):
    _safedelete_policy = SOFT_DELETE_CASCADE
    uuid = models.UUIDField(default=uuid.uuid4, max_length=36, null=False, unique=True, primary_key=True)
    followup = models.OneToOneField(Followup, null=True, blank=True, on_delete=models.CASCADE, related_name='exam', default=None)
    class Meta:
        constraints = [
            UniqueConstraint(
                fields=['followup'],
                condition=Q(deleted__isnull=True),
                name='unique_active_one_to_one_field'
            ),
        ]
    

[LECARROU]

A solution seems to change OneToOneField to ForeignKey and define UniqueConstraint in Class Meta as mentionned above.
But As ForeignKey reverse relation return a QuerySet and not a single object, I have to modify all my template to add ".first" to access a single Exam object from Followup object