It's a fairly simple and standard process via a Notaire. The property and any other land will need to be valued but the Notaire should organise this, other than that it's just a case of signing the documents and paying the fee.

Whatever the circumstances of the succession if it is the principal residence then the conjoint has the free right to remain there for one year, Article 763 du code civile, so there is no rush to declare the succession.

I was purchasing a property and the seller, a non resident English lady widowed several years before had not declared the succession, I was initially helping her out with things (she spoke no french) until it dawned on me that she did not want to declare the death and wanted to sell as if her husband was still alive, I think she was trying to disinherit one or more offspring.

I wasn't going to be party to any antics like that and to buy a property where the sale could be contested so I dropped out, a friend of hers told me that the sale went through during the confinement by electronic signatures etc, a false signature in the case of the defunt.