I think it's hard to determine what Trump believes and what he does not, and harder still to determine when he does or doesn't believe anything, since he is malleable and able, it seems, to convince himself of lies and deny truths even when directly presented with them. The problem with your doubt is that it involves two equally nasty alternatives (though they are not mutually exclusive either): To excuse him of the charge of just plain lying pretty much requires that he is delusional and stubbornly immune to reality, if not downright insane. Or, of course, you can consider him quite sane and aware of reality, in which case he's a consciousless liar.
There's no way, I think, that Trump comes out of the scenario we've seen unfolding here smelling good. He lost the election and claimed to win it. He attempted to subvert the democratic process in order to retain power. It's on the record. He spurned advice, and turned on advisors who insisted on recognizing reality and maintaining some integrity. It's on the record. And if his actions and statements were not incitements to violence and insurrection the only excuse is to aver that he was clueless about the supporters he had cultivated and incited over and over again, unaware of what he was saying, out of touch with reality, and, in short, dumb as a brick.
It's the same old dilemma. If you want to excuse Trump of malfeasance, the only real alternative is to attribute his actions to incompetence.