I am running Ubuntu 20.04 focal 64bit on a Dell Precision 7510. Here is what I have done so far.

kbest@kbest-Precision-7510:~$ sudo apt install curl # if you haven't already installed curl
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  libxmlb1
Use 'sudo apt autoremove' to remove it.
The following additional packages will be installed:
  libcurl4
The following NEW packages will be installed:
  curl libcurl4
0 upgraded, 2 newly installed, 0 to remove and 1 not upgraded.
Need to get 396 kB of archives.
After this operation, 1,123 kB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Abort.
kbest@kbest-Precision-7510:~$ sudo apt update
Hit:1 http://us.archive.ubuntu.com/ubuntu focal InRelease
Get:2 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]                                                                                                                                
Get:3 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease [108 kB]                                                                                                                              
Get:4 http://packages.ros.org/ros/ubuntu focal InRelease [4,679 B]                                                                                                                                        
Hit:5 https://download.virtualbox.org/virtualbox/debian xenial InRelease                                                                                                                       
Hit:6 http://archive.canonical.com/ubuntu focal InRelease                                                                                                   
Get:7 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]                             
Hit:8 http://archive.ubuntu.com/ubuntu focal InRelease   
Get:9 http://us.archive.ubuntu.com/ubuntu focal-updates/main Sources [528 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages [2,196 kB]
Err:4 http://packages.ros.org/ros/ubuntu focal InRelease                                   
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
Get:11 http://us.archive.ubuntu.com/ubuntu focal-updates/main i386 Packages [745 kB]
Get:12 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 DEP-11 Metadata [274 kB]
Get:13 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 c-n-f Metadata [16.0 kB]
Get:14 http://us.archive.ubuntu.com/ubuntu focal-updates/universe amd64 DEP-11 Metadata [405 kB]
Get:15 http://us.archive.ubuntu.com/ubuntu focal-updates/multiverse amd64 DEP-11 Metadata [940 B]
Get:16 http://us.archive.ubuntu.com/ubuntu focal-backports/main amd64 DEP-11 Metadata [8,024 B]
Get:17 http://us.archive.ubuntu.com/ubuntu focal-backports/universe amd64 DEP-11 Metadata [30.5 kB]
Get:18 http://security.ubuntu.com/ubuntu focal-security/main Sources [252 kB]
Get:19 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages [1,821 kB]
Get:20 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [40.7 kB]
Get:21 http://security.ubuntu.com/ubuntu focal-security/main amd64 c-n-f Metadata [11.2 kB]
Get:22 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [92.9 kB]
Get:23 http://security.ubuntu.com/ubuntu focal-security/multiverse amd64 DEP-11 Metadata [2,468 B]
Reading package lists... Done                    
W: GPG error: http://packages.ros.org/ros/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
E: The repository 'http://packages.ros.org/ros/ubuntu focal InRelease' is not signed.
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.

I think there is a problem with a missing Public Key. I am not a Linux power user by any stretch of the imagination so I don't know how to proceed.

when I try to execute:

sudo apt install-noetic-desktop
E: Invalid operation install-noetic-desktop

Any suggestions on how to fix the public key and then get a successful install?