Forgot the login password and not able to log into Endless OS with an existing user account.
Endless OS provides a unique online self-service to help users to recover from password lost:
Password Unlock Tool
On your computer, after typing in the false password:
On a secondary device with the Internet connection:
Go back to your computer,
And now you can log in to Endless OS with your new password
In case you don't want anyone or yourself to unlock the computer when losing the password, you can disable it.
pkexec --user Debian-gdm dbus-run-session gsettings set org.gnome.shell password-reset-allowed disable
A series of messages will appear in the terminal, including messages that appear as warnings/errors, however you should now find that the password reset functionality has been disabled.