This is how it’s typically explained to adopted children.
There are different parts of being a mother.
Biological - providing the egg and Gestating and giving birth to the baby
Legal - having the legal right as the child’s parent
Caring - actually parenting the child, caring for child on a daily basis
In some families, the same person does all three parts of being a mum.
In adoptive families, the adoptive mum does the second and third parts. The birth or bio mum does the first.
In some step families, the step mum does the third only. In other step families, she does have some legal rights or even becomes the adoptive mum.
But of course on this thread we are talking about surrogacy and not adoption. So In so called gestational surrogacy, the bio mum can actually be two different women.
In adoption we explain to children that none of their mothers is any more or less real than the others. The role of mother isn’t about feelings, it’s about facts.
That’s why the term “ real mother “ is particularly offensive, as it erases other women and denies the child’s reality.
A women who is a surrogate can say that she doesn't feel like a mother. She of course is entitled to her feelings. But they don’t change the law in her country. And she can’t compel everyone else involved to feel or believe the same as her.
A biological mother whose child has been adopted can feel that she is the real mother and the other/s are fake . But the law and reality say she is wrong. No one is fake, they just do different parts of being a mother.
Well meaning people can encourage an adult adoptee to “ find her real parents”. But their language doesn’t change legal documents or wipe out 20 years of parenting by the adoptive mother.
Feelings don’t trump biology or the law.
As we know, some people are trying to do that in other areas and it’s not working out well for women and children .