Use of undefined constant NONCE_SALT
Error message
Use of undefined constant NONCE_SALT ... in Shortcode.php on line 192
Cause & solution
The problem will be related to a missing constant in your wp-config.php file. This file should contain an automatically generated "NONCE_SALT" constant as you see here in the sample wp-config.php file:https://core.trac.wordpress.org/browser/tags/5.4.1/wp-config-sample.php
at this line:
define('NONCE_SALT', 'put your unique phrase here');
In your case this seems to be missing for some reason. You should generate a new one:
https://api.wordpress.org/secret-key/1.1/salt/
and enter it into the wp-config.php file as you saw above and that will fix the problem!