Course completion can be turned on in the course settings (turned off by default), but needs to be enabled at the site administration level first.
In Administration > Site administration > Advanced features check the "Enable completion tracking".
This gives you access to an activity completion menu in the course settings, and a few completion tracking reports. No need for any plugin if you use this.https://www.youtube.com/watch?v=G6vjgfMae8U
This video is a bit old but these functions haven't changed much since 2.3