Clearly, he doesn't want the vax.

It's fairly easy to buy a vax pass in Serbia, so I'd say he deserves credit for running this risk.

They gave him a visa, then cancelled it upon his arrival—with no new information. They took his phone (and his ability to contact his lawyers). They confiscated all his possessions, including his wallet. He refused to sign the visa cancellation order, and was detained for three days.

I would submit that this isn't about the rich and famous getting their way. Rather, if they can do this to the world's #1 tennis player, what can they do to you?

There's also a point to be made about whether such treatment would ever be meted out to, say, Roger Federer.

My guess is that someone at the federal level wanted to appear tough to justify the hardship the Australian government has put its people through. They picked Djokovic because he has been fairly adamant about not revealing his vax status. They didn't count on Balkan stubbornness. It bears remembering that Serbia stood up to the entire military might of NATO for almost three months. Djokovic spent those three months training in empty swimming pools. He once said the radiation from the depleted uranium in the bombs might have impacted him positively.