By stupidly easy, I mean as simple as doing a ready meal.

I have ADHD and I just can't make myself cook. Sometimes even ready meals are difficult.

I want to start meal prepping in a way.

But in a way where I just cook like, 3 separate meats and some separate veg, store them and just take what I want at the time and go.

Marinate chicken drumsticks in soya sauce an garlic, put salted broccoli nearby, put it to oven or airfrier.

Well different meats and vegetables cook at different rates and require different prep. Specifics would provide context for us.

Poached chicken breast - bring salty water to boil, put in your chicken breast, cover the pot, remove from heat, and let it it in there about 30 mins.

Batch prep once a week. Search for “batch cooking” or “batch meals” & there are lots and lots of results.
https://thethriftyfamily.com/batch-cooking-for-beginners/

look up sheet pan meals, but prepped ingredients if you can afford to do so, toss in the oven and set a timer.

you can buy a ‘baking bag’ that has seasonings and you just pop a chicken/chicken parts and some veg (carrots, potatoes, etc) into bag, put bag in roasting pan and put in oven.

You’ve pretty much described meal prepping. You could oven bake some chicken breasts on a sheet pan, chop up some fresh veg, and cook rice on the stovetop and you’d have food for the week.

Or if you can handle it, try marinating some chicken (or other protein) in one container, and having seasoned, chopped veg in another container (s), and when you want to eat, throw a handful of each on a sheet pan and toss with a little oil and bake on a sheet pan for 30 min at 350F.

Sheet pan roasts. Imo the only meals that actually "come together in 20 mins".

Preheat oven to 400F.

Break up or slice vegetable (many options: broccoli, asparagus, eggplant, zucchini, onion, carrot, parsnip, potato, butternut squash, etc) into pieces. Toss in a bowl with olive oil, salt, pepper, whatever seasoning strikes your fancy. Put into a sheet pan, if you want to save yourself the cleanup, use aluminum foil.

In the same bowl, toss in soy sauce (use in place of salt, often better than salt because extra umami) and whatever dried seasonings fit your mood. Mix into a slurry/paste. Add whatever quick-cooking cut of meat you have (salmon, chicken, pork loin, pork tenderloin, beef strips etc) and toss to coat. Throw onto a foiled sheet pan.

Wash one bowl, done. Do some other chore while the food cooks, 20-40 minutes depending on the size of each piece and all that.

Roast a whole chicken. cut up some combination of potatoes, carrots, broccoli, sweet potatoes, or brussels sprouts (or leave them whole if they are small), toss the cut veg in some oil, salt, and pepper, spread them out on a sheet pan--use parchment paper to line the pan--and roast them in the oven until you can stick a fork in them. The broccoli and the sprouts won't take as long as the hard vegetables so if you are using them add them about halfway through.

You can enjoy a nice meal of roast chicken and veg and refrigerate the leftovers. The next day pull the rest of the chicken meat off of the carcass and you can eat it plain or slice up and put in sandwiches or over a salad.

I always make stock from the carcass, skin, and scraps of chicken but I don't know how much interest you have in making a soup. It's an easy ADHD project because you can do it in phases--make the stock one day and then add leftover chicken meat and whatever else you want to have in your soup and then you have a nice pot of soup that you can portion out and eat whenever you want to.

The easiest would probably be something like an instant pot recipe where you just throw stuff in the pot and let it go and then portion it out when done; you can find a bunch by looking up "chicken veg rice instant pot" or something similar

If you're getting stuck on prep steps check your supermarket for pre marinated meats and pre chopped veggies. They'll be more expensive but saves you some steps and time

Foil covered sheet pan, lightly oiled for quick clean up. Pack of Italian sausages lined up in middle spaced slightly apart. Surrounded by oiled carrots, onions & potato chunks with salt & pepper. Roast at 350-400F until veg are at 200F & sausages reach 165F ^1.

1. Instant read thermometer or oven probe w/ alarm.

Chili beans are one pot, easy, can be cooked in large batches and frozen in smaller portions. Protein and fiber rich. I like to eat with some freshly cooked rice but it's a stand alone dish as well.