Why is my dishwasher leaving food gunk on everything all of a sudden?

Yeah that filter is meant to come out and get cleaned on a regular basis, and most people never know it's there until something like this happens. On most dishwashers it just twists a quarter turn counterclockwise and lifts out. Pull it out, scrub it under hot water with an old toothbrush and some dish soap, and while you're down there check the sump area where it sits because that gray sludge usally collects in the recess too. A slimy buildup like that will recirculate right back onto your dishes every cycle, which explains the grit in the cups. The spray arm comes off too on most machines. Usually it's either a snap-fit or held by a single nut you can turn by hand. Once it's off, run water through it backwards and poke the holes out with a toothpick or a piece of wire. Those dark holes you noticed are almost certainly clogged with gunk, and a blocked arm just sprays weakly at whatever it can reach.

Now the cloudy film on glasses is a seperate thing to watch. If it's a chalky white film, run some vinegar through a cycle and see if it clears. If the vinegar doesn't remove it, that's permanent etching from soft water and too much detergent, and no amount of cleaning fixes that. Worth checking before you assume it's the machine. If cleaning all that doesn't solve it, the next thing I'd check is water temperture. Pop open the door mid-cycle on a full wash and feel the water, or better yet check wheather the machine has a heating element and if it's actually getting hot. alot of these problems trace back to water that never gets hot enough, and quick wash cycles expecially don't heat properly. Also run your kitchen sink on hot until it's steaming before starting the dishwasher, so the machine fills with hot water instead of cold from the pipe run.

One more thing, stop pre-rinsing. Modern detergents actually need some food soil to work against, and a light scrape is all dishes need. Sounds backwards but it's true.

One thing I'd add after going thru this exact saga with my old machine is to verify it's actually filling with enugh water. Mine had the identical symptoms, gritty cups and half-clean plates, and it turned out the fill was running short, so the arms were spraying through barely a puddle. Open the door about a minute or two into the fill portion and see where the water level sits relative to the filter rim, then compare with whatever your manual shows. Also make sure the arms spin freely by hand after you reinstall them, since a warped rack or a stray bit of foil can wedge one and quietly kill half your spray coverage.

I had somethig like this happen and it turned out a chunk of broken glass had fallen into the bottom of the machine and was blocking one of the spinning arms from turning. It still sounded normal from outside so I had no clue until I took the arm off. Now I check under there whenever I break something near the dishwasher.

Also do the arms spin freely by hand when you push them? Mine whould kind of stick and that made half the rack come out dirty while the other half looked fine.

Back in the day the old machines had a hard food disposer in the bottom so you never even thought about a filter. Now they all rely on that trap catching everything, and folks go years without touching it. I pull mine every month or so and give it a scrub, takes two minutes. One old trick my mother used was a cup of white vinegar sitting on the top rack in a hot cycle once in a while to keep the tub from getting funky. Also, once you've got that filter out, take a flashlight and look in the sump hole for anything hard stuck down there, seeds and toothpicks love to lodge in those.

Gonna push back on the etching thing. Soft water causing a cloudy film seems backwards to me, in my area it's the hard water that leaves that chalky coating on glasses, and vinegar usually clears it right up. Ours was terrible until I started using a rinse aid and bumping the detergent amount down. Etching is real but it's way less common than people think, and it looks more like permanent frosty patches than a film you can wipe at. So if vinegar doesn't work don't assume the glasses are done for yet, try a cleaner made for hard water buildup first before writing off the whole rack.