This may be more of a question for the Matomo developers, but I thought some folks here must have gone through the install for Matomo since there are one or two plug-ins that use/support Matomo:

How do I add the matomo package to my public folder so that I can then view it (e.g. at mysite.com/matomo)?

I am able to wget it into /var/www/html where my site's code lives. However, when I add the matomo package there (with the folder named "matomo"), I cannot open the page mysite.com/matomo -- I get a 404 Page Not Found on my website.

If you are using Apache, you'll need to add an exception to your .htaccess file

For example, you can add this line below

##
## White listed folders
##
RewriteCond %{REQUEST_FILENAME} -f
# Allow Matomo
RewriteCond %{REQUEST_FILENAME} !/matomo/*