What is a legacy contact?
A legacy contact is a person you nominate inside a platform's own settings to access some of your account data after your death. Apple and Google both offer versions of this. It is configured within the service and works independently of your will.
Apple's legacy contact issues an access key, which the contact needs alongside a death certificate to reach the account. Google's inactive account manager works on a timer: after a set period of inactivity it notifies the people you chose and shares what you specified.
Both must be set up in advance by the account holder, and neither can be arranged afterwards by the family, however compelling the circumstances.
Nominating is only half the job. Someone has to know the nomination exists, and in Apple's case hold the access key. A legacy contact nobody was told about achieves nothing at all.