Is there any plugin which allows only to create new tags if user has 50+ reputation?
Yes. Tagging tools plugin here: https://github.com/svivian/q2a-tagging-tools
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
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April 20, 2021: Q2A 1.8.6 released!