Hi, another Austrian here! As someone already mentioned, Plum Village is a wonderful retreat center in France. There are also groups called Wake Up (https://wkup.org/) in Vienna and Graz that practice the teachings of Thich Nhat Hanh as a community. They are extremely open to guests and newcomers, so maybe you also want to check that out :)

Plum Village is in southwestern France, it was the first center to open. It’s a wonderful place.

https://plumvillage.org/

There is a really wonderful Buddhist center in Vienna affiliated with the same branch of Tibetan Buddhism I have gone on retreat with. They should have retreats as well. I recommend checking it out. https://gelugwien.at/

There is also the European Institute of applied Buddhism (EIAB) in Waldbröl, Germany https://eiab.eu/