It's premature to call dismissals in the DoD as a coup, but it's also worth remembering that democratic backsliding rarely happens with tanks rolling down the street these days. Let's take a look at Latin American from 2009 on:

Democratically elected leaders were impeached in Honduras, Paraguay, Brazil, and Peru (twice, and the latest one yesterday), and overthrown in Bolivia. All looked like civilian decisions on paper, but the military threat was obvious in Honduras, Paraguay and Bolivia.

Also, the justification was rather noble-sounding in all: punishing corruption, restoring democracy, etc. So, the textbook definition of a coup wouldn't necessarily hold. That's why context matters.

So all in all, let's recognize that what's happening in the U.S. right now is a huge anomaly that, if allowed to continue, will result in some form of democratic backsliding, even if the word 'coup' may not be appropriate.

One last thing: authoritarian actors are way more creative than they are given credit for. Neither authoritarian reversals nor ways to stop them can be copy-pasted from another country.