Filter_sanitize_string

My application with PHPRAD Classic is errored in the variable FILTER_SANITIZE_STRING.

What am I supposed to do?

I’m no expert but in my experience this comes from your running PHP ver 8 while the program generates ver 7. There will be other deprecation notices too.
To keep using PHP ver 8, in VSCode you can replace FILTER_SANITIZE_STRING with FILTER_UNSAFE_RAW
Good luck