Not able to post data through wp-admin

I recommend to try by debugging the code, might be there is an issue because of a New version of PHP.
Try by writing this code into the wp-config.php file and see what if any error:

 // Enable WP_DEBUG mode
define( 'WP_DEBUG', true );

// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );

// Disable display of errors and warnings 
define( 'WP_DEBUG_DISPLAY', true);
@ini_set( 'display_errors', 1 );

// Use dev versions of core JS and CSS files (only needed if you are modifying these core files)
define( 'SCRIPT_DEBUG', true );

NOTE: You must insert this BEFORE /* That’s all, stop editing! Happy blogging. */ in the wp-config.php file