One proof that the Second Amendment applies to individuals, NOT only militias is simple. Here is the Second Amendment:
A well regulated Militia, being necessary to the security of a free State, the
right of the people to keep and bear Arms, shall not be infringed.
Now, here is the Second Amendment in street language:
Because a self-governed army of civilians separate from the nation’s regular army is necessary to guarantee the freedom of Americans, PEOPLE (INDIVIDUAL AMERICANS, NOT ARMIES [GROUPS OF AMERICANS]) shall not be limited in their right to own and use guns, rifles, assault weapons, machine guns, bazookas, artillery, tanks, etc., etc.