The standard way to get rid of duplicates is:

my %seen;
my @filtered = grep !$seen{$_}++, @arr2;
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The difference is that you only want to remove duplicates of elements present in @arr1. Let's adapt the above:

my %seen;
my %in_arr1 = map { $_ => 1 } @arr1;
my @filtered = grep !$in_arr1{$_} || !$seen{$_}++, @arr2;
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