Did the notary charge us too much? Are the land registry costs too expensive?

Yes, it is true, we are obligated to build within 12 months and are not allowed to sell or rent out at the beginning.

Then I was charged the land charge twice?! (It is already on page 2)

Yes, once by the notary for the notarization of the property; once by the district court for the registration of the property.
That makes two times in total.

And then €750 for typing 2 minutes of data into the PC.... That only happens in Germany

Yes, that's just how it is. But if it soothes you, everyone else had to pay for it too.

The transaction value for the property purchase at the notary was 141,264.00 euros. The invoice from the land registry office shows a value of 153,036.00 euros. Shouldn't these values be the same? Where does the difference come from?

I would also like to know why that is different