It seems there are 3 versions of libproj: libproj12 (version 4.9.3) from openSUSE libproj12 (version 4.9.3) from the Application:Geo repository, now removed libproj13 (version 5.1.0) from the Application:Geo repository GRASS has a dependency on libproj12. Falling back to the openSUSE version still makes qgis crash. Forcing the removal of libproj12 (gives warnings about GRASS) resolves the crash of qgis: qgis now start OK.