From type/Allomorph

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method chop(Allomorph:D: |c)

Calls Str.chop on the invocant's Str value.

From type/Cool

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sub chop(Str(Cool))
method chop()

Coerces the invocant (or in sub form, its argument) to Str, and returns it with the last character removed.

say 'raku'.chop;                        # OUTPUT: «rak␤»

From type/Str

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multi method chop(Str:D:)
multi method chop(Str:D: Int() $chopping)

Returns the string with $chopping characters removed from the end.

say "Whateverable".chop(3.6);  # OUTPUT: «Whatevera␤» 
my $string= "Whateverable";
say $string.chop("3");         # OUTPUT: «Whatevera␤»

The $chopping positional is converted to Int before being applied to the string.