qr{^\s*[^#]*\s*sub}

##</code><code>##

#!/usr/bin/env perl

use v5.26;

my $re = qr{^\s*[^#]*\s*sub};

my (@match, @no_match);

while (<DATA>) {
    if (/$re/) {
        push @match, $_;
    }
    else {
        push @no_match, $_;
    }
}

say '*** Matched:';
print for @match;
say '*** Not Matched:';
print for @no_match;

__DATA__
should match these:
sub hello {
    sub hello {

should not match these:
#sub hello {
#    sub hello {
    # sub hello {
    #     sub hello {

##</code><code>##

*** Matched:
sub hello {
    sub hello {
*** Not Matched:
should match these:

should not match these:
#sub hello {
#    sub hello {
    # sub hello {
    #     sub hello {