Tell me, why didn’t you go to the actual source. The Unites States Department of Defense?
Apparently, you did not bother to read the links. All of them in fact direct readers to the DOD directive. It is discussed in historical context and it's purpose and role.
“The provisions in DoDD 5240.01 are not new, and do not authorize the Secretary of Defense to use lethal force against U.S. citizens, contrary to rumors and rhetoric circulating on social media,” Sue Gough, a spokesperson for the Department of Defense, told VERIFY.
"Department of Defense directives are not laws or executive orders – they are policy statements. In other words, these directives can’t make something legal if it isn’t authorized under federal law or by the Constitution." Nunn and Goitein of the Brennan Center for Justice explained.