How can I get the WYSIWYG editor to appear when using CiviCRM with Wordpress on Cloudron?
This is because your cms.root doesn't match properly with civicrm.root variable and you might be using variables in Resource url for 'CiviCRM Resource URL'. 

For such cases you add below two line at the end of the file you will need to change 

$civicrm_root = '/app/data/wp-content/plugins/civicrm/civicrm/'; to $civicrm_root = '/app/code/wp-content/plugins/civicrm/civicrm/';

$civicrm_setting['URL Preferences']['userFrameworkResourceURL'] = CIVICRM_UF_BASEURL . 'wp-content/plugins/civicrm/civicrm';civicrm/';                                                                                                     
$civicrm_paths['civicrm.root']['url'] = CIVICRM_UF_BASEURL . 'wp-content/plugins/civicrm/civicrm';civicrm/';


Thanks

Pradeep