if ($str =~ /^(\d{2,4})[^\d](\d{2})/){     // no error by perl -Tcw

Please note that in Perl regex syntax, \d{2,4} and \d{2} are counted quantifiers and are perfectly valid. This is very ancient and very common syntax, so let's hope it's never deprecated! (Pay no attention to the Raku behind the curtain.)