Apt Update Error - Focal Fossa No Longer Supported

Question

I am getting the following error when running 'apt update' on my Ubuntu 20.04.3 LTS machine.:

The repository 'http://security.ubuntu.com/ubuntu focal-security Release' no longer has a Release file.

I looked up what it means by 'focal' and that translates into Ubuntu 20.04 (which is the most current LTS release at the time of posting).

How can the most recent LTS release, which I believe should be supported for five years, no longer be supported?

This is the full output from sudo apt update and lsb_release -a:

$ sudo apt update
[sudo] password for administrator:
Hit:1 http://nz.archive.ubuntu.com/ubuntu focal InRelease

Get:2 http://nz.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]

Get:3 http://nz.archive.ubuntu.com/ubuntu focal-backports InRelease [101 kB]

Get:4 http://nz.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages [1,170 kB]

Ign:5 http://security.ubuntu.com/ubuntu focal-security InRelease

Get:6 http://nz.archive.ubuntu.com/ubuntu focal-updates/main amd64 DEP-11 Metadata [282 kB]

Get:7 http://nz.archive.ubuntu.com/ubuntu focal-updates/universe amd64 Packages [851 kB]

Ign:8 http://ppa.launchpad.net/certbot/certbot/ubuntu focal InRelease

Hit:9 http://archive.canonical.com/ubuntu bionic InRelease

Err:10 http://security.ubuntu.com/ubuntu focal-security Release

  404  Not Found [IP: 31.170.160.150 80]
Get:11 http://nz.archive.ubuntu.com/ubuntu focal-updates/universe amd64 DEP-11 Metadata [351 kB]

Get:12 http://nz.archive.ubuntu.com/ubuntu focal-updates/multiverse amd64 DEP-11 Metadata [944 B]

Get:13 http://nz.archive.ubuntu.com/ubuntu focal-backports/universe amd64 DEP-11 Metadata [10.3 kB]
Err:14 http://ppa.launchpad.net/certbot/certbot/ubuntu focal Release

  404  Not Found [IP: 91.189.95.85 80]
Reading package lists... Done
E: The repository 'http://security.ubuntu.com/ubuntu focal-security Release' no longer has 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 'http://ppa.launchpad.net/certbot/certbot/ubuntu focal 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.
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.3 LTS
Release:    20.04
Codename:   focal

Checking the IP:

$ dig @8.8.8.8 -t any security.ubuntu.com
; <<>> DiG 9.16.1-Ubuntu <<>> @8.8.8.8 -t any security.ubuntu.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 64332
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;security.ubuntu.com.       IN  ANY
;; ANSWER SECTION:
security.ubuntu.com.    59  IN  AAAA    2001:67c:1562::18
security.ubuntu.com.    59  IN  AAAA    2001:67c:1562::15
security.ubuntu.com.    59  IN  A   91.189.91.38
security.ubuntu.com.    59  IN  A   91.189.91.39
;; Query time: 288 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Mon Aug 23 22:25:57 NZST 2021
;; MSG SIZE  rcvd: 136

$ dig -t any security.ubuntu.com

; <<>> DiG 9.16.1-Ubuntu <<>> -t any security.ubuntu.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10286
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;security.ubuntu.com.       IN  ANY

;; ANSWER SECTION:
security.ubuntu.com.    19  IN  A   91.189.91.39
security.ubuntu.com.    19  IN  A   91.189.91.38

;; Query time: 16 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon Aug 23 22:30:44 NZST 2021
;; MSG SIZE  rcvd: 80