FWIW I get syntax errors with that code on Perl versions back to v5.22.4.

The change: https://perldoc.perl.org/perl5220delta.html#A-literal-%22%7b%22-should-now-be-escaped-in-a-pattern.

"f you want a literal left curly bracket (also called a left brace) in a regular expression pattern, you should now escape it by either preceding it with a backslash ("\{" ) or enclosing it within square brackets "[{]" , or by using \Q ; otherwise a deprecation warning will be raised. This was first announced as forthcoming in the v5.16 release; it will allow future extensions to the language to happen."

Update: marto beat me to it ...