When attempting to migrate term sets or term groups, one of the following messages is displayed:

When migrating managed metadata, it is strongly recommended to have 'Term Store Administrator' permissions on your source site.
​When migrating managed metadata, it is strongly recommended to have 'Term Store Administrator' permissions on your destination site.

Term Store Administrator permissions are needed to read all required information from the source and to update the destination environment accordingly.
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When performing a migration with managed metadata, we recommend getting Term Store Administrator permissions on the source and the destination, even if you have higher-level admin permissions such as global or SharePoint admin.

Get Term Store Administrator permissions at the source and destination before copying managed metadata.

For more info, see the Microsoft article Assign roles and permissions to manage term sets.