For users of Manjaro, since last update available since 05/12 Mixxx do not start due to new Protobuf version.
A workaround of this issue is to create a sim link to older protobuf in system library like this as root user:
ln -s /usr/lib/libprotobuf-lite.so.27 /usr/lib/libprotobuf-lite.so.26
Works fine on many machines under Manjaro.
Remember and note this modification in case of conflict situation to be able to remove this link.