That is not true. National popular elections still rely on the same voting booths with known numbers of local voters. A location with a thousand voters turning out a million votes would be instantly detected and investigated.

Someone wanting to swing a national popular vote fraudulently would need to compromise tens of thousands of ballot boxes to steal on the order of ten million votes -- a much harder ask than compromising a hundred ballot boxes to swing three states in the Senate/Electoral College or gerrymandering twenty districts in Congress.