Seems that Biden invalidated most all Trumps executive orders when he took office e, can’t Trump invalidate bidens, including pardons, just as easily?
No. Pardons are not executive orders. Executive orders are not even mentioned in the Constitution. Pardons are. Once given and accepted, they cannot be revoked. I do not know if they can be revoked before being accepted, but I expect not. And subsequent presidents can do nothing about a pardon granted by a previous president.