Paul
First, are you running your website on Plesk or cPanel or Virtualmin?
Secondly did you do a manual install of the database and WP files to your file manager or did you use a script like Softaculous 1 touch install?
Third what Theme are you using? Is there a special customization section for settings based on the theme?
I can’t think of any reason in general why the WP Settings –> General website url or alternate url would be grayed out? that doesn’t make much sense unless there is another factor at play