How to grant Unmask permission to a user at table level and column level in sql server?
Unfortunately, there is no granularity for the UNMASK permission in SQL Server, users either see all masked data as masked or unmasked depending on whether they have UNMASK granted.

You could create a low-privilege user that has SELECT and UNMASK and create a stored procedure to retrieve only the columns you're after into a temporary table while impersonating this user. These results can then be joined back to your masked table after reverting the impersonation so that the columns that should be masked are and those that should be unmasked are retrieved from the temp table.