Trump and Biden are not in the same team, in the sense that they represent opposing parties, who benefit (and their members) from holding the power.
Beyond that, they are both just presidents, e.g. when it comes to foreign affairs mostly figureheads for the long term American foreign policy, which is dictated by national "interests", the state department, and long term (career) washington personel, not by who happens to be the president now or then.
From that aspects, they're just mascots for different teams, playing the same sport, where others are calling the shots.
>But if they're the same team, then why did Trump mind losing the election
Because parties like winning.
>why the big lie
Nt such a big lie. Even if not widespread election fraud, the whole game was rigged against him, regarding press coverage, assosiates investigated (for the same kind of deals and BS that's daily business on from both sides for decades, but nobody bats an eye), supposedly neutral organizations standing against the president, double standard reporting as "unprecedented" for the same shit Obama, Clinton, Bush and co pulled, and so on.
>why attempt a coup?
A couple thousand rag-tag fans got in the capitol, with no plan, no leadership, no endorsement, and no prospects. It was just a BS protest attempt from idiots. But of course it got played to death as some kind of evil coup plan - from the same press that hailed an equally incompetent senile bland long-term insider as the second coming of Lincoln.