I am getting it to run with ssh -Y -X and using the -k option, mfix -k and at least the GUI opens:
However I still see these errors:
QStandardPaths: XDG_RUNTIME_DIR points to non-existing path '/run/user/xxx', please create it with 0700 permissions.
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast
mfix - WARNING - The vtk module is not available, can not create vtk window
mfix - ERROR - Error saving file: write() argument must be str, not None
mfix - WARNING - The vtk module is not available, can not create vtk window
mfix - ERROR - Error saving file: write() argument must be str, not None
Error saving ui state write() argument must be str, not None