2021-06-08 - Christian Hesse

Starting with libxcrypt 4.4.21, weak password hashes (such as MD5 and SHA1) are no longer accepted for new passwords. Users that still have their passwords stored with a weak hash will be asked to update their password on their next login.

If the login just fails (for example from display manager) switch to a virtual terminal (Ctrl-Alt-F2) and log in there once.