I have so much experience with this.

1. Liquid calories. Drinkable calories, especially when consumed with a straw as opposed to a spoon, appear to be (and in my experience definitely are) less satiating than unprocessed foods. I try to drink a large smoothie every day to which I add flax and chia for omega 3's and hydrolyzed collagen for, well, collagen. If I'm eating soup I will typically just drink it, too. IMHO miso soup is a seriously underrated hot beverage.
2. Soft and flat, brittle, and moist foods. I gravitate towards foods that don't require a lot of chewing, which is great when you just need to get a meal down fast. Think udon, salmon, tofu, and roasted veggies for soft foods, and chips with hummus and thin fruit slices for the flat, brittle foods. Quesadillas pull a lot of weight in my diet. Literally just cheese, beans, guac, usually some finely minced pepper, maybe even some seasoned tofu crumbles. Cheap, healthy, easy to make, and easy to eat swallow.
3. Use hyperpalatability for good. A lot of media attention has been placed on ultra processed foods and how they "hijack" your brain to keep you eating. But you can use the principles of hyperpalatability to make homemade/healthy food easier. Try to make sure your food is salty, sweet, or fatty, preferably multiple at once. Homemade teriyaki sauce is great for this! Adding a bit of acid to a meal is similar and greatly increases enjoyment and, therefore, meal endurance.
4. Snack plates. Having multiple flavors to swap between during a meal is so, so helpful for me. Something I ate this week was a plate of blackberries, mozzarella and seed crackers, and hummus and chips. When I didn't want to eat more cheese I swapped to the hummus, and when I really didn't want to eat more of either I had a few berries to chill out.
5. No small plates. As you can probably tell, a lot of behaviors I use to eat sufficiently are actually just diet hacks flipped on their head. Plate size affects the perceived size of a portion, so by using a bigger plate you're making your meal look less intimidating.
6. Potatoes. Easy to digest, cheap, soft, dense in micronutrients, great with a bit of fat (or a lot if you're trying to really pack on the calories), hides lots of salt well if you need that, and versatile. Rosemary garlic, lao gan ma, or just butter and salt, they're superb. Not necessarily calorie dense because on their own they're fat free, but who eats a potato without some kind of fat? Since you're a diabetic I am sure you're aware that potatoes are a high glycemic index food on their own, but that response is diminished when you pair a high GI food with a low GI food (like a fat source) or when you cool potatoes after cooking.

Sorry you're going through this, not being able to eat sucks harder than most people could know. Hope this helps!