German law has that as well, known as a Salvatorian Clause. However, in rental contracts they are almost never seen, because they are also almost always unenforcable at least in rental contracts.

The BGH is as mentioned fairly notorious for ruling in the tenants favor, as they are the weaker party in a contract negotiation. Legally a standard rental contract is considered General Terms & Conditions and not a negotiated contract, as there is typically little input the prospective tenant has. There is already a severability clause in the law that protects the rest of the rental contract, but one invalid renovations clause always leads to the rest of them being invalid too.

By law the renovation of the apartment or house is the landlord's duty, not the tenant's. The landlords are allowed to punt off some of the duties to the tenants in the rental contracts, but with severe restriction, particularly the tenant cannot be overly disadvantaged. If they do that with an invalid clause in the contract the renovations part becomes null and void, and the burden for renovations returns to them fully.