First of all, Welcome to the forums. Hopefully you will enjoy TrueNAS and the forums.
You need to provide some details such as what specific version of TrueNAS you are running.
Please read the following:
Also, have you performed an internet search for the problem? I did and in about 10 seconds I was reading about this issue on many different forums. Here is one: avahi logs "avahi_normalize_name() failed" · Issue #658 · avahi/avahi · GitHub
Google is a very easy way to find previous problems and then hopefully those lead to a solution.
I am not trying to be mean to you, I am trying to teach you to fish. It is much better if I can teach you how to find solutions quickly vice waiting on someone to read your posting.
Good luck and I hope you solve the issue quickly as it does get annoying when the log fills up with the same message non-stop.