suityou01

'supports'          => __( 'title', 'editor', 'excerpt',
                                        'author', 'thumbnail', 'comments',
                                        'revisions', 'custom-fields', ),

should be

'supports'          => array( 'title', 'editor', 'excerpt',
                                        'author', 'thumbnail', 'comments',
                                        'revisions', 'custom-fields', ),

Then it works. I get basic post entry form. Need my custom fields to show too, but that is out of scope for this ticket.

The game changer was the debug log, so thank you for the pointer on how to set this up.

Thanks for getting back to me so quickly and with so many things to try.

There are no js errors in dev tools.

The output of the post entry form in html is as follows

<div id="post-body-content">

</div>

So no css trickery.

Removing capability_type made no change.

When I turn on debugging I get the following warning when I refresh the add custom post page

Warning: foreach() argument must be of type array|object, string given in /var/www/html/wp-includes/class-wp-post-type.php on line 665 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-includes/class-wp-post-type.php:665) in /var/www/html/wp-admin/includes/misc.php on line 1438 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-includes/class-wp-post-type.php:665) in /var/www/html/wp-includes/functions.php on line 7108 Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wp-includes/class-wp-post-type.php:665) in /var/www/html/wp-admin/admin-header.php on line 9

I only have 3 plugins enabled

Akismet, CodeMirror Blocks, Hello Dolly