Disable PHP parsing of HTML files

I have a 500 error on a Apache/PHP-FPM site due to an XML declaration that triggers the PHP parser:
<?xml version="1.0" encoding="UTF-8"?>

I need to disable parsing of PHP from HTML files. I tried with a .user.ini file with the engine off directive, but it did not work.

What is the suggested way to disabe handling of HTML files by PHP?

pecus this should work in .htaccess:

<FilesMatch \.html$>
    SetHandler none
</FilesMatch>