Quoter:

By having the error message A partner claim with id 'identifier' is not found , it is primarily due to neither of the inherited policy [Base or Extensions] provides the output claim of email from the orchestration step 1 that is prerequisite of GenerateOTP technical profile (TP) input claim [partner claim identifier in your policy].

If I understand correctly, as you are using SelfAsserted-LocalAccountSignin-Email TP for signin, then the signInName carries only email that you can copied into email claim type just before invoking Generate OTP profile for resolving the issue.