It occurs to me that if this situation were reversed and happening in say, Venezuela, USA would be claiming a coup had already taken place.
So far we have:
Failure to accept the result
Excluding the legitimate winner from information on security and Covid
Pushing ahead with budget planning for 2021
Secretary of State planning for inauguration of Trump's 2nd term
Hasn't the coup already happened?
No, it hasn't already happened.
Failure to accept the result - the official results aren't technically out yet. The apparent results are, well, obvious to most anybody, but they aren't technically done yet.
Excluding the legitimate winner from information on security and Covid - this is a dick move, but it's not a requirement to share that information. And it's not uncommon for access to that information be delayed while the results are being contested - it was delayed for Bush too.
Pushing ahead with budget planning for 2021 - I'm less certain here, but I'm under the impression that budget planning for the coming year routinely starts in the prior year, even if that's an election year. I don't think this is at all out of the ordinary, and IIRC, the incoming president has opportunity to make budget adjustments once he takes office.
Secretary of State planning for inauguration of Trump's 2nd term - I'm currently planning for a major effort at work, for a thing that is contingent. The thing itself may not happen, but planning has to go forward as if it were certain, otherwise we wouldn't have time to get it done. That may not be the case here, but I'll refer you back to item 2, and remind you that it's Trump, so a jackass move shouldn't surprise anyone.
And at the end of all of that... The coup hasn't actually happened, because, well, it' hasn't actually happened. Trump has not stayed in office beyond his term, the election results haven't been overturned or ignored. You might think that Trump is in the process of attempting a coup, which is your prerogative, but it still hasn't yet occurred.