Change Ubuntu's purple login screen to GNOME 3.36's

Question

My login screen on boot is Ubuntu's purple login screen. On suspend, the login screen is GNOME's new one, with the blurred desktop bg. How can I get rid of Ubuntu's and only have GNOME's?

• Settings app reads: Ubuntu 20.04 LTS, GNOME 3.36.1.
• /etc/X11/default-display-manager reads /usr/sbin/gdm3, though I don't know what's the default in the Wayland case.
  
• sudo gdm3 --version reads GDM 3.34.1 (why not 3.36.1?)

Note: On Ubuntu's log in screen I can pick GNOME (which I use)/GNOME Xorg/Ubuntu/Ubuntu Wayland. I have a feeling this is related, and I'd basically like to get rid of everything Ubuntu (other than the OS ofc) and only keep GNOME.

EDIT: a video / screenshots showing the GNOME lock screen at the beginning changing to the Ubuntu one after clicking the Switch User button.

Thanks in advance.

Answer 1

Ok.. your video made it clear.

for this acheivment you need to run the below command and choose the corresponding number for this file. /usr/share/gnome-shell/gnome-shell-theme.gresource

sudo update-alternatives --config gdm3-theme.gresource 

Example output:

    $ sudo update-alternatives --config gdm3-theme.gresource 
    [sudo] password for admin: 
    There are 4 choices for the alternative gdm3-theme.gresource (providing /usr/share/gnome-shell/gdm3-theme.gresource).

      Selection    Path                                                           Priority   Status
    ------------------------------------------------------------
      0            /usr/share/gnome-shell/theme/Yaru/gnome-shell-theme.gresource   15        auto mode
      1            /usr/local/share/gnome-shell/theme/blur.gresource               0         manual mode
      2            /usr/local/share/gnome-shell/theme/focalgdm3.gresource          0         manual mode
    * 3            /usr/share/gnome-shell/gnome-shell-theme.gresource              10        manual mode
      4            /usr/share/gnome-shell/theme/Yaru/gnome-shell-theme.gresource   15        manual mode

Press <enter> to keep the current choice[*], or type selection number:

To remove the "UbuntuLogo" image from the screen, open the file /etc/gdm3/greeter.dconf-defaults and navigate to this section..

# Login manager options
# =====================
[org/gnome/login-screen]
#logo='/usr/share/images/vendor-logos/logo-text-version-128.png'

and uncomment the last line.. which should look like this..

# Login manager options
# =====================
[org/gnome/login-screen]
logo=''

or if you wish to put your own image..

# Login manager options
# =====================
[org/gnome/login-screen]
logo='/home/admin/myubuntu.jpg'