My honest opinion is that Trump wanted a BIG rally to demonstrate that he had a lot of support to make the idea that he lost to Biden seem absurd. He used this reasoning over and over again, even in his call with the GA SoS.
Occam's Razor makes that far easier to believe than that he wanted people to take over the capitol building. Beyond just sounding like crazed conspiracy, it doesn't even make any sense to do. What is he gonna do with a building? Like, what if they managed to take congresspeople or senators hostage? How in the world would that lead to maintaining his hold on power?
Sorry, it just sounds like a bunch of conspiratorial claptrap to me, along the lines of the stuff I hear from the right with their Q and Lin Wood nonsense. The crazy thing is that it's become institutionalized on the left in the MSM. It's bonkers.