Trump has neutered the usual criteria for endorsing a political candidate:
“I have known Dr. Oz for many years, as have many others, even if only through his very successful television show,” Trump said of Oz.
Donald Trump endorsed Dr. Mehmet Oz in his bid for Pennsylvania’s open Senate seat, the former president announced Saturday.
nypost.com
In other words, Trump hasn't even met the guy.
And, God, how silly it seems to remember the crap Reagan and Schwarzenegger, and some other athletes and astronauts got for being mere celebrities running for public office with no experience, but they had a certain measure of integrity. Trump's endorsements don't require that.
Oz, of course, has his own special qualification to attract Trump's support:
https://www.huffpost.com/entry/dr-oz-congress_n_5504209
After all, Oz is a grifter quite a bit like Trump.