You can find the download in the Resources area of this website.  Just click on Sage 50 Canada (main forum at the top of this page), then on the right, click on Product Resources and follow the links.  There should be a download article in the Knowledgebase as well.

If the computer that is already updated was updated as you closed Sage 50, then on that computer, you should be able to find the installation program (single file) in this folder:

C:\Users\Public\Documents\Sage Software\Simply Accounting\Download

and in the c:\Sage folder (unpacked installation program).

Lastly, it's not completely evident as it is happening but no one is "forced" to install.  The default settings are to download and install, but you can change that behaviour under Help, About Sage 50...., Support Info, Modify Product Update Settings.

Also, if you haven't changed that behaviour, you can stop the installation if you are "forced" to start it.  There is a Cancel or Exit button (I can't remember the exact terminology used).  Cancelling an installation of a new version does not affect the current version installed.

Your second computer is likely telling you there are no updates because you didn't install 2023.