It's a Non-Issue -- Biden/Harris Couldn't "Pack" the Supreme Court Even if They Wanted to

Congress, not the president, decides how many seats there are on the Supreme Court.

The president can ask Congress to increase or decrease that number.

The president can sign legislation increasing or decreasing that number if Congress sends him or her such legislation.

Otherwise, the president is powerless.

As is the vice-president, other than the possibility of casting a tie-breaking vote on such legislation in the US Senate.