Biden is likely to enter his first term as president with a divided Congress, where Democrats control the House of Representatives but Republicans hold a majority in the Senate.
It really does seem quite likely that the Democrats will continue to be in the minority in the Senate, and hold on to a majority in the House even after losing four seats. This last seems certainly worthy of note: far from enjoying a Blue Wave, the Democratic Party managed to lose four House seats after four years of Trump, after a year of a pandemic, historic unemployment.