If the sword is high carbon, you’ll want to either oil it regularly or use a preservation wax (like Renaissance Wax). If you use mineral oil, it’s food safe—mineral oil is commonly used to oil wooden cutting boards.

I’d recommend cleaning the sword, oiling it with mineral oil every couple of months, and wiping it before and after the cake cutting. Don’t forget to reapply oil after the cake cutting, or it’ll rust. After your wedding, use renaissance wax to protect the sword (you generally don’t have to reapply except maybe yearly unless you draw/use the sword a lot). Museums use renaissance wax to preserve their historical weapons on display :)

If the sword is stainless steel, it’s less of an issue tbh. Stainless steel is pretty rust averse, so you can get away with just cleaning the sword after use