Without a license and a passport. Who are stateless people?

Can your Russian passport be taken away for an anti-war post on the Internet? According to the new law, yes, if your citizenship is acquired. But there are already tens (and possibly hundreds) of thousands of stateless people living in Russia. In a country where a piece of paper is needed for every sneeze, their fate is unenviable. Who are stateless people, where do they come from, and how can you end up among them?