The problem is that you need to get
my $regex2 = qr% \n
(?:
\QI'll be good.\E
 Hushing
 Hrumph
 \Q>:[\E  \Q:(\E  \Q:(\E  \Q:c\E  \Q:c\E  \Q:<\E  \Q:<
+\E
 \Q:[\E  \Q:[\E  :\{  \Q:\E  \Q:@\E  \Q>:(\E  \Q:'(\
+E
 \Q:'(\E
 \QShutting up now.\E
 \QBut, but...\E
 \QI'll be quiet.\E
)
%mix;
But, as curly braces are the delimiters, qr{ \{ } turns into qr% { %', , but there's no way how to express 'qr% \{ % with curlies as the delimiters  but you don't need that, as they're equivalent.
That's why I don't like using curlies as regex delimiters.
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
my @res = ( qr% a{1 %,
qr{ a\{1 },
qr% a\{1 %,
qr% a\Q{\E1 %,
qr{ a\Q\{\E1 },
qr% a{{1}1 %,
qr{ a\{{1}1 },
qr{ a\{{1}1 },
qr{ a\{\{1\}1 },
qr% a\{{1}1 %,
);
say $_, ' a{1 ' =~ $_ for @res;
Update: more examples in the second code.
($q=q:Sq=~/;[c](.)(.)/;chr(5+lengthSq)`"SoS2"`map{chr +ord
}map{substrSq`S_+`}3E`7**23:)=~y+S`+$1,++print+eval$q,q,a,
