Your opinion requested / unmarried financing

There is no right and no wrong. Usually, it is simply overlooked that the woman works part-time, supports the man, and then stands alone afterwards.
Get advice
Find a fair arrangement with and without children before the divorce war starts
Build your house and never need the arrangement for a separation.

Possibly you keep your higher equity in reserve or only contribute part of it (40,000 euros more than your partner).

If you get advice, also think about protection in the event of death. I find it terrible when a family really loses everything. Very few can manage the loan alone, especially if the person has to reduce to part-time because of children.

€40,000 more than the partner is the "free amount" that does not count as a gift, or is still within the limit there?

No, the exemption amount is 20,000. Since both of you are listed on the land register, the value of the house, land register is divided 50/50, you can contribute 40,000 more. 20,000 for you + 20,000 for your girlfriend.

If the basis for this is that the ex only made it possible through their work, e.g. to afford a certain installment amount, then honestly I wouldn't see why I should feel greater sympathy. Without the ex, such a house would never have been possible...

The assets of some men would look different if they only worked 75% and took their share of raising the mutual children.

Apart from the fact that sympathy is not appropriate anyway, I definitely did not want to start a "man vs. woman" discussion, but merely point out that the situation is complex. The idea of undertaking a construction project as partners without a marriage certificate in a partnership is basically very welcome.