It's a mere anecdote and YMMV but I've had the onboard coffee and tea with a variety of airlines many times over the years and to memory it's never given me trouble.
This varies significantly from person to person, yeah.
I was fine for years until I wasn’t - now I basically restrict myself bottled water and wine, which come from outside the plane. Many airlines flown in the past year around the world too.
Another problem with that is we don't know what made us sick. And if we think airplane coffee is fine but didn't like lunch at the diner, we tend to assume it's the latter.
