Were large German warships strengthened for ice?

Were the larger German ships of the Second World War strengthened for sailing in ice?

No, not as a general design feature.

The larger German ships of the Second World War are not described as specially strengthened for ice sailing. No class-by-class construction comparison or discussion of ordinary cold-weather operation is provided. The supported boundary is narrow but useful: service in northern waters should not by itself be treated as evidence of an ice-strengthened hull.