I want to grep the list of hash references

Indeed, but @{$remote_list}->{filename}} is not a list of hash references. That's in @remote_list according to what you said, so your grep will look like

grep { ... } @remote_list
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So how you decide if a reference matches or not? By checking "its" filename against $file.

grep { $_->{filename} eq $file } @remote_list
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But that's very inefficient. If you have 4 remote files and 5 local files, you are doing 4*5=20 comparisons when there's no reason to do more than 4.

my %local_files = map { $_ => 1 } @local_files;
for (@remote_files) {
   print "match\n" if $local_files{ $_->{filename} };
}
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