I rented out my place for one year. The tenant wants to extend for half a year. Can I agree to this without risk?

No. You run the risk of the rental agreement automatically changing into a rental agreement for an indefinite period. And the tenant might be entitled to full rent protection.

It is possible to rent out residential accommodation for a limited period of time up to a maximum of 2 years with reduced rent protection. However, this is subject to strict conditions, for example, the rental agreement cannot be renewed. If you do so anyway, the rental agreement automatically changes into a rental agreement for an indefinite period and the tenant is entitled to full rent protection.

Consequence: You need a legal ground for termination to terminate the lease and the consent of the tenant or the court.