As I read it:
“The purpose of the Posse Comitatus Act – in concert with the Insurrection Act of 1807 – is to limit the powers of the federal government in using federal military personnel to enforce domestic policies within the United States.”
Surely any lawyer worth their salt or any person with common sense could argue that preventing a foreign invasion from outside the US is not a domestic issue.
PC does not apply to NG activated by Governors.
You can use Title 10 personnel on the border even under the current circumstances. I’d guess their are at least 50 or so intel guys there. And perhaps some air units, maybe ground units but not in direct proximity to the border. But to use them for surveillance, patrols or other like military missions vs the invasion, takes a few more hoops. Even for drug activity.
“enforce domestic policies within the United States”