No Release File

[bsmither]

I get the following lines when running :
sudo apt update
according to the instructions on this page:
https://nginx.org/en/linux_packages.html

-----
Err:10 http://nginx.org/packages/mainline/ubuntu tricia Release             
                                  
  404  Not Found [IP: 95.211.80.227 80]

E: The repository 'http://nginx.org/packages/mainline/ubuntu tricia 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.
-----
Am I missing some understanding on following these instructions?

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,287202,287202#msg-287202