Did they ever serve any food at the diner?

A big salad

Yes, lots of food - George often yelled things like 'I am going to need a chocolate pudding here!' or something along those lines.

Remember the episode about the pilot of their TV show, where Elaine is 'coming down with something', and Jerry is trying to eat, but Elaine ends up stealing his food and explaining she thought he was done, and Jerry replies something like 'How am I done, I took two bites?', then offers the food the woman, whose name I am not going to research how to write correctly right now, but something like Gail Cunningham?

Kramer first snubs that woman, then kisses her. NBC's boss becomes ill from eating the pasta primavera that Elaine sneezed on.

In that episode, we can clearly see Elaine eating Jerry's food, and Jerry is appalled that she would do that, especially when she's 'coming down with something'.

The 'coffee shop' as they call it (not a diner - there IS a diner episode in the 'The Bubble Boy' episode, with the 'Nothing's finer than being in your diner'-slogan, but that's a different story) indeed does sell all kinds of foods and bubble gum as well.

Remember Newman ordering food there and remembering Kramer's buttery skin and imagining him as a chicken or something? Remember Jerry asking a cop if he could protect him from Crazy Joe Davola (not sure if this is spelled correctly), and the cop orders a muffin as well?

There are NUMEROUS times they eat food there, how many episodes have you watched so far, one?

Flopped in syndications???!!! Jerry and Larry would uproariously laugh at that statement, but they probably couldn't hear it from on top of their mountains of money.

They haven't made a new episode in over 22 years. The fact that it's still on syndication is a huge win. And consider how much it was on over the past 2 decades. TBS used to have a whole night dedicated to Seinfeld from 6pm-midnight. Then factor in DVD sales, which didn't start until 2004 I believe. And the fact that it's on Netflix means they are still getting paid for it. And if Hulu wanted it, that means there was a bidding war for it, and probably will be again when its current deal expires.

Even if Seinfeld was pulled from all streaming platforms and never aired another episode anywhere ever, not only would it still not be a flop, but it might be the most successful syndicated show ever.

Sept. 2019 - Netflix acquires future rights to Seinfeld.
Oct. 2021 - Seinfled airs on Netflix.

Oct. 2020 - Investor's Business Daily reports on a Netflix stock price drop coming off a weak earnings report. Lots of other stocks dropped that week, and no mention in the article at all of Seinfeld.

How on earth have you linked these events? (Actually, I'm not sure I want to know.)

Comedy Central dedicates HOURS to Seinfeld. I wish I liked the show a lot more than I do, along with Friends and a few others. I'd be entertained constantly, but alas .... :(

"Plus, you're coming down with something? Want a bite?"

Yes, they ate a lot.

However, it was not a DINER. It was a COFFEE SHOP.

There is a diner in the Bubble Boy episode, though - and there's nothing finer than being there.

The show never explicitly mentions it (that I recall) but I'm pretty sure both George and Kramer suffer from rather unpleasant flatulence, that Jerry is pretty much on full alert whenever they come in that he may want to move them somewhere downwind pretty quickly. Elaine too, but in bursts... Both George and Cosmo are long haul truckers from the beginning of the series to the end... Elaine mostly emits when she's dancing. I guess they were just trying to sneak by the censors. The show does make it obvious that Jerry is a bit of a neat freak, so the whole thing makes for a wonderful subtext, if that is, you don't mind earthy humor. Personally, I abhor it, and never enjoyed that show.

Don't hate the bait, if anyone hate the troll.