The error you're getting is not because %count doesn't exist.

$ perl -e'my $count{abc};'
syntax error at -e line 1, near "$count{abc"
Execution of -e aborted due to compilation errors.

$ perl -e'my %count; my $count{abc};'
syntax error at -e line 1, near "$count{abc"
Execution of -e aborted due to compilation errors.
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Therefore, the issue isn't a lack of autovivification. If it somehow made sense to do my $count{'abc'}, you might be right that %count should be autovivified.

What you are trying to achieve can be done using

my %count = ( abc => 0 );
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