I am married under the separate property regime. My wife and I live in an apartment that I own. I want to sell it and the notary tells me that my wife's consent is required. Is it true?

Yes. This rule is intended to protect the family home and applies even when this property belongs to one of the spouses only. In the absence of your wife's consent to this sale, she could request the cancellation within one year from the day she became aware of it and at the latest one year after the dissolution of the matrimonial property regime (art. 215 paragraph 3 Civil Code.).