Have a read of this thread - Contact form does not work with PHP 8.0
Check to see if your web server is running PHP 8.0 and if it is, try reverting to 7.4 and see if that solves the problem.
Have a read of this thread - Contact form does not work with PHP 8.0
Check to see if your web server is running PHP 8.0 and if it is, try reverting to 7.4 and see if that solves the problem.