There are several sites, which claim that dash cams are illegal in Austria and, in fact, in a number of European countries:
https://gb.snooper.eu/blog/can-i-use-my-dash-cam-in-europe/
However, there appears to be discussions elsewhere, which say they are OK:
https://www.quora.com/Why-is-using-a-dash-cam-illegal-in-Austria
Can anybody tell, what is actually the case?