PHP Deprecated: Constant FILTER_SANITIZE_STRING is deprecated

Getting many PHP Deprecated notices in error log in various lines on a client website:

[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2070
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2075
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2079
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2082
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2085
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2092
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2093
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2105
[20-Oct-2023 16:20:11 UTC] PHP Deprecated:  Constant FILTER_SANITIZE_STRING is deprecated in .../wp-content/plugins/event-post/eventpost.php on line 2106

Seems FILTER_SANITIZE_STRING ist not supported any more.

Event Post 5.8.6, WordPress 6.3.2, PHP 8.1.x