Sperm donation and the mitzvah of fertility and reproduction

According to this, does the one who donates sperm commit a void ejaculate? Or is it because the sperm is intended for fertilization (even if it does not ultimately occur) then it is not a void ejaculate. And another question, let's assume there is some sin in donating sperm, does this mean that fulfilling a vow in this way is considered a sin and therefore not considered a mitzvah?
With blessings,

I think it's really not a nullity. Even if he were not considered halakhically the father, I'm not sure it's a nullity. It's creating a child who will be someone else's seed.
If the mitzvah is from the donor, then it's a mitzvah that results in a transgression. If the mitzvah is from someone else (who is the father), there's room to believe that it's not. But as I said, it's clear in my opinion that the donor is the father.

Do you think there is any prohibition against sperm donation? Is it appropriate?

Obviously this is problematic. The sperm is not for nothing, but there is adultery at hand here and reflections are forbidden. Therefore, even if a donor is only because of the distress of a couple who cannot give birth. And even in such a situation, I think it is better for a married man to do this with his wife.
We need to check how this is done in practice and find out from those who are familiar with the facts and constraints.

I ask because on the one hand you said that the one who donated is fulfilling the mitzvah of Pur, and on the other hand you said that if there is a transgression in this, then there is no Pur because there is a mitzvah here that comes with a transgression, so how does all of this fit together?

I didn't understand the question. I answered your question that while there is a transgression here, it is a mitzvah that comes with the transgression. But there is no transgression here if it is done in the right way and for the purpose.

Another question is, if someone donates sperm in the usual way (i.e., not a married man who does it with his wife), can he fulfill a pur by doing so? Or is it because there is adultery involved and contemplation is forbidden, then is it a mitzvah that leads to a transgression?

If there is no one else who can do this, perhaps he is permitted to do so in order to help the couple in need, and then there is no offense here.

But in practice, there is always someone else who can. Furthermore, donations are usually made anonymously, when there is no connection between the recipient and the donor at all.

In such a situation, it is certainly possible that this will be the next mitzvah in transgression. It depends on the limits of the מהבע.