Can't install software via Ubuntu GUI. Neither Snap Store (orange icon) nor GNOME Software (blue icon) are able to search or show any installed apps.c

Question

The "Explore" tab loads properly for both. "Installed" is just empty. "Updates" says "Software is up to date"

I'm behind a proxy server at work running Ubuntu 20.04 on a Dell desktop.

Of note, when I open the "Software & Updates" app then click on the "Livepatch" tab, it tells me "Livepatch requires an internet connection."

I've already configured and updated my proxy info in the terminal and under Settings -> Network. There it does show a working wired connection.

I have been able to download software on the terminal without issues.

Output of sudo apt update:

Ign:1 https://desktop-download.mendeley.com/download/apt stable InRelease
Ign:2 https://github.com/retorquere/zotero-deb/releases/download/apt-get ./ InRelease                        
Err:3 https://github.com/retorquere/zotero-deb/releases/download/apt-get ./ Release                          
  Could not handshake: An unexpected TLS packet was received. [IP: 10.30.0.112 8080]
Err:4 https://desktop-download.mendeley.com/download/apt stable Release                                      
  Could not handshake: An unexpected TLS packet was received. [IP: 10.30.0.112 8080]
Hit:5 http://mirror.wiru.co.za/ubuntu focal InRelease                                                        
Hit:6 http://ppa.launchpad.net/smathot/cogscinl/ubuntu focal InRelease                  
Hit:7 http://dl.google.com/linux/chrome/deb stable InRelease                            
Hit:8 http://ppa.launchpad.net/teejee2008/ppa/ubuntu focal InRelease
Hit:9 http://mirror.wiru.co.za/ubuntu focal-security InRelease
Hit:10 http://mirror.wiru.co.za/ubuntu focal-updates InRelease
Reading package lists... Done
E: The repository 'https://github.com/retorquere/zotero-deb/releases/download/apt-get ./ Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'https://desktop-download.mendeley.com/download/apt stable Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Output of sudo snap install hello-world

error: unable to contact snap store

After writing these command I got a different error:

sudo snap set system proxy.http="http://10.10.110.128:8888/"

sudo snap set system proxy.https="http://10.10.110.128:8888/"

error: cannot install "hello-world": Post https://api.snapcraft.io/v2/snaps/refresh: proxyconnect
       tcp: tls: first record does not look like a TLS handshake

Did I make the problem better or worse?