@avolfart if you have downloaded the binaries and source from Brainstorm download page then the updates we pushed today might not be reflected. Check this Version mismatch for compiled binary on BST website - #2 by Raymundo.Cassani.
You can download the latest updated source code from GitHub - brainstorm-tools/brainstorm3: Brainstorm software: MEG, EEG, fNIRS, ECoG, sEEG and electrophysiology and try running it again using MATLAB