Camera movements are way too fast for your modern mouse with high DPI resolution, even if you set in-game mouse option to minimum? Here is the solution...

Edit the file "%USERPROFILE%\Documents\ArcaniA - Gothic 4\inputsettings.xml" (you can use Notepad etc.) and change the original line to:


Done.
Now you can finally adjust in-game Settings for mouse sensitivity within a reasonable range using the slider.

Are the camera movements with the mouse not smooth and a bit jerky?
Try this, using NVidia Profile Inspector:
2 - Sync and Refresh
Ultra Low Latency - CPL State = Off
Ultra Low Latency - Enabled = Off
Vertical Sync = 1/2 Refresh Rate (this will halve your screen refresh rate, so for a 144Hz screen for example you'll run the game at 72pfs, perfectly smooth. Try with/without.)