Just asking in curiosity. do all lab 4th gen hiv negative tests need to be confirmed by a second test, even if the first test is done outside the window period? or is one hiv test outside of 6 weeks enough?

No. Unlike the earlier antibody-only test, a positive AgAb (4th generation) HIV test is conclusive without any confirmatory test. Almost everyone with a new positive result goes on to have other tests, including an HIV RNA blood test. But the purpose is not primarily to confirm the AgAb result but to measure viral load, the main indicator of treatment effectiveness.