As a matter of curiosity, I tried some of the classic regexes mentioned in this thread that threaten exponential explosion. They seem to have been tamed long ago. (Same results for version 5.30.3.1.) What are some examples that can still go exponential?

Win8 Strawberry 5.8.9.5 (32)  Thu 10/07/2021 16:15:36
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -l
my $futile = 'a' x 10_000;

print 'start     ', scalar time;
die 'huh?' if $futile =~
    /a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a
+*a*b/
    ;
print 'post rx 1 ', scalar time;
die 'huh?' if $futile =~
    /(?:(?:(?:(?:(?:(?:(?:(?:(?:(?:(?:(?:(?:a*)*)*)*)*)*)*)*)*)*)*)*)*
+)*b/
    ;
print 'post rx 2 ', scalar time;
print 'done      ', scalar time;
^Z
start     1633637901
post rx 1 1633637901
post rx 2 1633637901
done      1633637901
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