Trump made several mistakes that day:
1) Held rally on same day as the vote and Dems took advantage of that fact to infiltrate the rally and get people to head to the capital and turn it into a “mob rally”. Optics is everything. He should have held a rally when Capital was closed. The people being held on charges most likely wouldn’t be in jail or waiting to be sentenced or charged if that had been done.
2) He took way too long to make a speech about what was happening and not condoning it.
I don’t believe he held or organized the rally. I think Stop the Steal organized it and invited Trump to speak. But I understand your point.