Unfortunately, there is no free plugin that will make a backup or download copy of a subsite on a WordPress multisite like https://webdesign.cci.utk.edu.There are several plugins, such as Duplicator, that include this as a paid feature.
Given these limitations, the best way for you to back up your site’s data is to use the WordPress export tool.
There are also ways to make local copies of websites that don’t involve the export tool or a WordPress plugin.
6 Tools to Download an Entire Website for Offline Reading