why Niederreiter cryptosystem is not a candidate in NIST PQC competition? Seemingly, Niederreiter cryptosystem is faster than McEliece, and it can also be used to implement digital signature. Why isn't this scheme appear in NIST post quantum competition?
Classic McEliece is using the Niederreiter T-OWF:

The KEM is built conservatively from a PKE designed for OW-CPA security, namely Niederreiter’s  dual  version  of  McEliece’s  PKE  using  binary  Goppa  codes.

https://classic.mceliece.org/nist/mceliece-20201010.pdf