From the Wikipedia Category Undeciphered Historical codes and ciphers - 'A list of unsolved problems that are, or are thought to be, codes or ciphers.'
- Beale ciphers
- The Blitz ciphers
- D'Agapeyeff cipher
- D-Day carrier pigeon cipher (links to the National Pigeon Service page)
- Dorabella Cipher
- European Voynich Alphabet
- Fenn treasure (discovered 2020)
- Kryptos
- Markovian Parallax Denigrate
- Olivier Levasseur
- Papyrus Oxyrhynchus 90
- Ricky McCormick's encrypted notes
- RSA Secret-Key Challenge#
- Shugborough inscription
- Taman Shud Case
- Unfavorable Semicircle
- Voynich Manuscript
- YOGTZE case
- Zodiac Killer
These are described further on the other Voynich Wiki [1].
There are many websites on the subject of uncracked codes and ciphers - eg [2], [3] and the Elonka's List page [4]. The lists share many entries in common.
See also Ciphers, Useful websites and materials and Undeciphered writing systems