In addition to impeachment, President Biden can assign new seats to the SC.
The court was stacked by not allowing Obama to nominate a judge in the last year of his term and then reversing that and allowing Trump to do so in the last couple weeks.
Also, the Senate refused to hear any nominations for lower federal courts from Obama.... 100+ vacancies weren’t filled due to Senate obstructionism.
The courts are stacked with right-wing hacks. So the Republicans certainly have no leg to stand on criticizing anything the Democrats choose to do, as long as the Constitution allows.