How to make middle and suffix matching using full text search?
The "Full" in Full Text Search means match full words, not parts of words

You should use RegExp or LIKE or tri-gram matching instead

You can mimic suffix matching by reversing words in your index and also reversing your queries, but this takes more space:

select
reverse('brown fox')::tsvector @@ (reverse('rown') || ':*')::tsquery --true