If you know, please also provide relevant documentation.

UPDATE (2025-02-02T06:06Z): I did some brute-force testing, and, at least for sh.itjust.works, it seems that the maximum username length is 50, and the maximum password length is 60 [1].

References
  1. “Sign Up”. sh.itjust.works. Lemmy. Accessed: 2025-02-02T08:49Z. https://sh.itjust.works/signup.
    • When creating an account on sh.itjust.works, the sign-up form will throw this error if the provided password is greater than 60 characters in length.
  • Kalcifer@sh.itjust.worksOPEnglish
    3·
    9 hours ago

    […] The lemmy-ui will truncate passwords beyond 60. So even if you have a 64 char password it will drop the last 4 and do the hashing on that.

    At least on sh.itjust.works, it doesn’t just silently truncate the password; it throws an error [1]:

    References
    1. “Sign Up”. sh.itjust.works. Lemmy. Accessed: 2025-02-02T08:49Z. https://sh.itjust.works/signup.
      • When creating an account on sh.itjust.works, the sign-up form will throw this error if the provided password is greater than 60 characters in length.