I found this Using .htaccess with FastCGII tested this and it loads the errordocument I have in .htaccess file.
PHP handler = fcgi, PHP version 7.4
it says you have enable AllowOverride in httpd.conf ?
maybe you can read this one and try it
Apache will read .htaccess files as long as AllowOverride is enabled in httpd.conf. What you cannot do is put PHP directives inside .htaccess: this works only with PHP installed as an Apache module and would cause a 500 Server error with PHP installed as either CGI or FastCGI.
Some configurations (with suphp and similar) allow for a per-directory php.ini with local settings. If this doesn't work with your setup you can change php.ini settings only with a series of ini_set() instructions (in an included file, most often)
just trying to Help ??