Marketing lists have the ability to be locked or unlocked by changing the value of the Locked field.
Members cannot be added to or removed from a locked marketing list. There are certainly times where it is appropriate to lock a marketing list, but doing so may interfere with various Click Marketing Automation functions, such as adding members to a marketing list using a Form action or Campaign Automation action. Locking a marketing list can also cause the Click Import tool to return an error if you attempt to use the Import tool update a marketing list.
You can toggle a marketing list between locked and unlocked by changing the value of the Locked field.
NOTE: If you are not the owner of the locked marketing list, be sure to consult the owner before unlocking it.
NOTE: When creating a static copy of a dynamic marketing list, Power Platform will automatically set the static list to locked.