If the election was rigged, why wasn't the Senate manipulated?
I'm willing to be there's a distinct possibility that John James in Michigan and Jason Lewis in Minnesota were cheated out of a win. I also suspect there was some fraud in North Carolina, but simply not enough to have Biden and Cunningham defeat Trump and Tillis.
I don't think they needed to cheat to defeat Gardner in Colorado and defend Shaheen in New Hampshire, though I'm suspicious of New Hampshire having that much of a disparity for Trump after being so close last time.
In Maine they don't seem to have any shady big-city apparatus - there's the possibility that they cheated somewhat there but it wasn't enough to overcome Susan Collins' crossover appeal to those who vote Democrat. Maybe Jared Golden in Maine's 2nd District was illegitimately re-elected and maybe Trump did better overall in that state.
In Montana they also don't have a big city apparatus, but maybe Trump/Daines/Rosendale/Gianforte had bigger wins in reality.
They may try cheating Loeffler and Perdue in Georgia though.
Keep in mind that there were apparently a great deal of "Biden only" ballots in multiple states. Smells fishier than Kamala's crotch.
tl;dr they definitely tainted the Senate races with voter fraud but it wasn't enough to unseat some GOP candidates, just because Trump and GOP candidates won in multiple areas does not mean there wasn't fraud in those areas that kept their victory margins from being even bigger; and they would cheat to flip those two Georgia Senate runoffs if they can get away with it