To what extent is the hadith "Whoever separates from the Community by a handspan has removed the yoke of Islam from his neck" authentic? And if it is authentic, what is its meaning and what is intended by "the Community" therein? Is it the religion or a specific community?

The meaning of the hadith (definition) is that whoever separates from the Muslim community by abandoning the Sunnah (definition) and following innovation, and by abandoning obedience to the Imam, has indeed removed himself from the ties of Islam. The ribqah is the rope by which a camel is tethered, and the Muslim's departure from the community is like a camel's breaking free from its tether, which exposes it to destruction and loss. What is meant by "the community" here is the community of Muslims that has an Imam whose obedience is obligatory, and not other groups.