Unbelievable error ..

Quite so - it is indeed very hard to believe. Your code as posted works fine:

$ cat 11149222.pl
#!/usr/bin/perl
use strict;
use warnings;
 
print "Content-type: text/html\n\n";
 
print "Hello World!";

$ perl 11149222.pl
Content-type: text/html

Hello World!$ perl -v | head -3

This is perl 5, version 34, subversion 0 (v5.34.0) built for x86_64-li
+nux-thread-multi

$
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