Yes, I agree that was an attempted coup.
It's not like there was election day, and responsible people suddenly realized there is strong evidence for fraud, and observers reported irregularities.
No, it was Trump himself who said weeks before the election that he will only accept the result if he wins. Long before the election even took place, he started talking about fraud without the slightest evidence to back it up.
And when he lost, he then repeated this baseless claim over and over again, despite all independent and partisan observers reporting no considerable irregularities out of the ordinary, and all important authorities from both parties confirmed the results.
It's pretty obvious that Trump spewed this lie -- and it was just that --, because he knows there are certain people who will believe every word he says, despite all evidence to the contrary. Obviously, he was hoping he could use these people to exert enough pressure on the system to be able to cling to power against the determined will of the people.
It's an attempted coup by the playbook of wannabe tyrants in banana republics or autocratic leaders in corrupt broken shithole countries, such as Putin, Lukashenko or Erdogan.
It's pretty sad that America, which once was admired abroad for its values of freedom and republicanism, and its shining example of a stable democracy, doesn't seem to care for its own values anymore, but joins the company of such failed states.