Everyone does that to be fair. My Spanish sources say they don't say much apart from positivo, focuus and the like.
I'm not sure how useful they are tbh. Alcaraz was an all-court natural as soon as he picked his racquet up basically. JCF may have lived past his use date.
Also he's pretty decent without JCF around. Has masters 500s and an Olympic gold match without JCF. It was when he came back sid Alcaraz lose actually. He did fine without even his physio around.
I'm spanish. Love to hear when JCF coaches him.
Sometimes is just "
this is the time to raise focus/intensity". Other times it is more tactical like "
play lobs with less pace and wait for the chance" (this was against Sinner on IW) or "
don't risk the down-the-line, the fast cross-court forehand is harming him too" (this was Cincy), or "
place yourself more to the left on the ad return, he's got trouble finding the T", or "
play more dropshots so that he does not sit so comfortably behind the baseline".
Things look very different when seen from the outside than during match play.
Don't fool yourselves. Coaching has always existed. Back before coached was allowed they used to employ non-verbal communication to give hints about serving and returning strategies. Also, coaching exists for everyone, not just Carlos.