In SQL Developer, click Tools, then Preferences, then Migration: Identifier Options, and ensure that the setting is correct for the Is Quoted Identifier On option (that is, that the setting reflects the database to be migrated).
I did some research. No good news. There is an Enhancement Request open to get this improved in SQL Developer. Please read the following note from My Oracle Support:
How To Migrate Non-Oracle Databases To Oracle With Case Sensitive Object Names Using SQL*Developer ? (Doc ID 1292434.1)
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