I’ve recently learned of a group Unitarian Christians in German-speaking countries. I can’t quite get a sense its theological center, but based on its links seems to fall in the “biblical Unitarian” camp, which is more conservative than the American Unitarianism in living memory. This focuses on biblical proofs of the unity of God, an interest in the theologically-Socianian Racovian Catechism (their version in German) and a recognition of the Christadelphians.
It’s only a few years old, but has centers in the north and west of Germany, and two churches that meet occasionally in Linz and Salzburg in Austria. Much of the activity seems to be online. Best wishes to them.
Reminds me of the Church of God General Conference. Last year they held a conference within an easy drive of where I live. I was almost tempted to attend, if only to see “the path not travelled”.