You can opt-in for a "no visual echo" of any character (asterisk or not) for password prompts:

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For KDE:

    sudo vim /etc/sddm.conf.d/hide-password.conf

insert in:

    [Greeter]
    ShowPasswordEcho=false

then reboot.

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For `sudo`:

    sudo vim /etc/sudoers.d/password-no-visual-echo

Insert/replace `Defaults` with:

    Defaults !pwfeedback

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For GNOME, you have to modify `unlockDialog.js`

    sudo vim /usr/share/gnome-shell/js/ui/unlockDialog.js

And do one of the following (version-specific):

    this._passwordEntry.clutter_text.set_password_char('');

or in newer version, replace `echo_char` with `null`. Reboot required.