I don’t understand this Legacy Contact

How to add a Legacy Contact for your Apple ID - Apple Support

A Legacy Contact’s access to your Apple ID is limited as described in Request access to an Apple account as a Legacy Contact - Apple Support

This tells you how to use the feature if you are a contact for a person who is deceased.

You may add, notify, or remove a Legacy Contact for your Apple ID as described in How to add a Legacy Contact for your Apple ID - Apple Support . A Legacy Contact’s access to your Apple ID is limited as described in Request access to an Apple account as a Legacy Contact - Apple Support .

You may remove a Legacy Contact for your Apple ID as described in How to add a Legacy Contact for your Apple ID - Apple Support This appears to be the same for somebody wishing to remove somebody else as a legacy contact, or a person wiching to remove themself as a legacy contact. Note that no notification may be sent to the other person so you may wish to notify them of this yourself if you want them to know of your decision.

Remove a Legacy Contact

You can remove someone as a Legacy Contact at any time in your Apple ID settings.

+ On your iPhone, iPad, or iPod touch, go to Settings > [your name] > Password & Security.

+ On your Mac, choose Apple menu  > System Preferences, then click Apple ID and select Password & Security.

Under Legacy Contact settings, choose the contact’s name to see more options.

Tap or click Remove Contact to remove them as a Legacy Contact. They won’t receive a notification of your decision, but you won't appear in their Legacy Contact list if they have an Apple device that includes this setting. The access key they received when you added them will no longer work.