This is a Salesforce known limitation with global picklist. You cannot convert an existing field from regular picklist to global picklist.

It is likely that your source org was manually converted to use global picklist (via workaround) and your target org is still using standard picklist. When you deploy, Salesforce attempts to convert the existing field in the target org to use global picklist but it couldn't because of the above limitation.

Manually convert the field in the target org via the following steps:

1. Create a new field and use global picklist.
2. Remove the old field.
3. Rename the new field to match the old field name.

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