Transfer 50% share of the house to a girlfriend

has been negotiated that way. The structure is clear so far... It is only about the tax perspective.

Alternatively, one could also consider a donation, and the renovation will be covered by her.

The real estate transfer tax is based on the values being transferred, therefore real estate transfer tax also applies in the case of a gift - otherwise in Germany there would be no purchases, only gifts. ;)

The cohabitation equivalent to marriage can under no circumstances benefit from marital allowances?

die eheähnliche gemeinschaft kann unter keinen umständen in den genuß von ehelichen freibeträgen kommen?

Probably not. There is no such thing as being a little married.

how is the real estate transfer tax calculated? normally based on the purchase price. Could I now simply set a purchase price equal to the exemption amount? Then my girlfriend would only pay 20000. Of course, I would be transferring my share too cheaply. However, it could be that she bears a higher share of the renovation costs without this being reflected in the purchase contract