Isn't social security (like social security bureau) a national local institution? Why do you see many forms of companies on the Internet? Can they handle such a thing?

Many companies on the Internet are just intermediaries and agents. They provide some paid agency services for social security procedures, but they are not social security agencies.

What needs to be clarified is that people often refer to "social security department" as "social insurance agency" under various names. There are institutions called XXX Social Insurance Bureau, XXX Social Insurance Fund Administration, XXX Social Insurance (Labor Insurance) Company, XXX Social Insurance (Medical Insurance) Center, etc. Is an institution managed by civil servants. (Note: XXX is a place name)

As for the "Social Security Bureau", it refers to the "Human Resources and Social Security Bureau", which exercises the functions of the former Labor Bureau and Personnel Bureau and is established as a national administrative organ with the same name throughout the country.