Deprecated commands

l love WN Flipbox but have had to deactivate it because now when I sign in to my back end (Dashboard) I get the errors listed below while using version 6.5.2. I’ve deactivated all plugins then enabled them one at a time to discover it was this one causing the following errors while working in/on by backend.(Dashboard).

Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated in /home3/createdp/public_html/wp-includes/functions.php on line 7288

Deprecated: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in /home3/createdp/public_html/wp-includes/functions.php on line 2187

Deprecated: strpos(): Passing null to parameter #1 ($haystack) of type string is deprecated in /home3/createdp/public_html/wp-includes/functions.php on line 7288

Deprecated: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in /home3/createdp/public_html/wp-includes/functions.php on line 2187

Warning: Cannot modify header information – headers already sent by (output started at /home3/createdp/public_html/wp-includes/functions.php:7288) in /home3/createdp/public_html/wp-admin/includes/misc.php on line 1439

Warning: Cannot modify header information – headers already sent by (output started at /home3/createdp/public_html/wp-includes/functions.php:7288) in /home3/createdp/public_html/wp-includes/functions.php on line 7096

Warning: Cannot modify header information – headers already sent by (output started at /home3