Best way is to send the drive to a reputable data recovery firm .... This is a drive with USB PCB and most likely have bad sectors + slow issue ... (firmware problem) ...
Can you show us S.M.A.R.T. attribute screen capture ? Maybe you have pending sectors + re-located sectors ?
Again those drives are not easy to work with ... Maybe you should consult with someone who knows what she/he is doing and do have tools to extract your data safely while the heads are still working ...
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