Well, you might’ve entered the password incorrectly a few times, and then faiilock faillocked the account. Can be fixed by going to another tty (e.g. Ctrl+alt+f3), logging in as root and faillock --reset --user your_username_here. If that doesn’t help, that’s probably neon’s issue (mb they messed up pam stuff or something).
On a side note, KDE neon is not exactly stable for daily driving, I’d suggest switching to another distro that’s not meant for testing recent KDE stuff