Ok, working solution - for me at least.
Delete the contents of your data directory and nextcloud install directory
Create a database user and database and assign with all permissions using your cpanel/whm
Download and extract into your nextcloud directory the zip file download “nextcloud-12.0.3.zip” rather than the setup php file
Browse to your url and give it an admin name and password, change the data directory if you wish and use the database you just set up instead of sqlite
Everything is working as it should now
Not sure if it was permissions, setup php, sqlite, used admin menu to change my background or changed the skeleton folder contents - that’s an investigation for another day.
(Once you’ve confirmed this works can you mark this as the solution as this seems to be an issue several people have experienced and it will likely help them too)