I have Frequent Traveller Status with the Miles & More programme and bought an economy ticket for my next flight with Austrian Airlines. The Miles & More website seems to indicate that I can use the business lounge with this status, but the Star Alliance website indicates that I need Gold Status (equivalent to M&M "Senator") for lounge access, whereas Frequent Traveller equates only to Silver.
Does that mean I get lounge access at Vienna for my Austrian flight but maybe not for other Star Alliance partners? Does this apply for my return flight from Heathrow as well?
Correct, lounge access for M&M Frequent Travellers is an M&M specific benefit, not Star Alliance related. So you get access to Lufthansa group lounges when you are flying on a Lufthansa group flight (this includes Lufthansa, Austrian, Swiss, Brussels and Eurowings).