https://www.senate.gov/history/partydiv.htm

Information about Current Senators Party Division 118th Congress • Majority Party: Democrats (48 seats) • Minority Party: Republicans (49 seats) • Other Parties: Independents (3 seats)

According to the .gov website, the independents caucus with the Ds, and that's how the Ds have the senate majority.

senate.gov

Information about Current Senators Party Division 118th Congress • Majority Party: Democrats (48 seats) • Minority Party: Republicans (49 seats) • Other Parties: Independents (3 seats)