As far as I know DeSantis isn’t running.
He's not yet but the primaries and caucuses aren't really going to start for another year.
Exactly. Did I miss DeSantis’ campaign announcement?
Well, now that Trump has announced, there's no reason for DeSantis not to say "I'm not running" if that's his intent. And he hasn't said that.
So my guess is either that he already has decided to run, and is just waiting until next summer to announce, or hasn't yet decided and is keeping his options open depending upon how things go between now and then.