Upvote:4
Italy is part of the Schengen travel zone and so is Austria. The UK is not.
This condition must be fulfilled every single day. There is no reset. After 90 days in, you must stay 90 days out. (On the 181th day you could come back in since the first of the 90 days in was more than 180 days ago.)
But you are not a resident of the Schengen zone, I believe.
Important: If you are an EU citizen who lives and works in Italy for clients elsewhere in the EU, you might already be an Italian resident for tax purposes. Talk to a competent tax counsellor now.