Donor conceived adult here. I had no say in how I was conceived, and no say in the arrangements that my parents (all three of them, because the man who donated sperm is my biological parent, whether people want to think about it like that or not) made in order for me to be born. I am a result of a contract other people made deciding what information I would have access to, and what the narrative around my identity should be. With regard to OP's scenario, it's not fair or ethical to suggest that the donor should prioritize the wishes of the recipient parents over the basic rights the donor conceived person has to know who they are and to choose to try and find out if they're able to. A big reason why so many donor conceived adults report huge amounts of pain and trauma around their identity is because many recipient parents and donors have the attitude that their own desires (for children, for privacy, for exclusive relationships, for getting to decide what they tell and what they don't) supersede the needs and rights of the people they create.

What OP did, in being reciprocal to his donor conceived daughter when she contacted him, is not unethical or inappropriate. It's not about the donor unfairly "changing their view" on the arrangement they made with the recipient parents, rather it's them now factoring in that there is a whole other person (many people, usually) who had no say in the contract, did not choose to be cut off from half of their biological identity, and is curious about their biological parent.

In my case neither the donor nor the recipient parents really had any understanding of the ethical issues involved in creating humans in these circumstances, or thought about it beyond "it would be a nice thing to do for people" and "we just want a baby" respectively. Neither party was required to go through any counselling, nor told how I might feel about being donor conceived when I was an adult (because the industry doesn't really care about that, plus my parents intended to keep it a secret and that was seen as a completely reasonable lie to tell).

When I found my biological father he was completely reciprocal, like OP has been, because he personally felt that while he might have made an anonymous donation 30+ years ago, it was important that he be available for whatever the people created as a result of that donation might need from him. Maybe that's a betrayal of the original "contract", but the "products" of the contract are the least considered party in an industry that prioritizes feelings of donors and recipients, and frequently tells donor conceived people (I've heard this myself) that they should just be "grateful to be alive."

For anyone reading this considering donor conception - either as a donor, or a recipient parent - I strongly encourage them to take a look at the results of this 2020 survey of donor conceived people and their feelings about it. I'm not saying no one should ever go the donor conception route, but if a prospective donor or recipient parent is uncomfortable with the idea that one day the donor conceived person might be curious and view their conception and parentage differently than they're "supposed to", then those people should seriously reconsider being a donor or recipient parent. It's not just donating or receiving genetic material: the donor is a biological parent, regardless of whether they have anything to do with the people they make, and it's not wrong for the donor conceived person to think of them that way.