TL;DR I turned the offending line into a comment by adding a ˋ#ˋ in the first column and restarted Apache.
To fix this, I followed the Youtube tutorial and opened up the file "httpd-autoindex.conf" using Finder and navigated down to line 21 which has the error. It reads Alias /icons/ "/usr/share/httpd/icons/".
Then I found this tutorial by just searching ...
By following the tutorial, you have created the file /etc/apache2/users/username.conf which contains the following:
Options Indexes MultiViews FollowSymLinks
Require host localhost
(note that you've replaced "username" with your actual username)
If you want to allow the public ...
You can compile your own httpd version and make a new LaunchDeamon and point Server App to your httpd in the httpd_server_app.conf:
Disable the com.apple LaunchDeamon as shown above:
$ sudo launchctl unload -w /Applications/Server.app/Contents/ServerRoot/System/Library/LaunchDaemons/com.apple.server.httpd.plist