> Would you call every other leader selection process where the US has given their support for a candidate a coup?

That's clearly a mischaracterization of what happened in Ukraine. Yes, Washington declared its support for the opposition in Ukraine. It also:

- bragged about spending $5 billion funding the opposition over preceding years.

- participated closely in the Yalta European Solution for decades, which was a forum for Washington power brokers + Ukrainian oligarchs.

- endorsed the overthrow of Yanukovych (i.e. by not demanding his democratic government was restored, which e.g. Washington did in Niger recently).

- and so on

It was a coup. It was primarily achieved through covert action, which by definition avoids yielding smoking guns that would cater to your personal, precise, technical definition of "coup", but given the totality of the circumstances we can only conclude that it was a coup.