How can I gain weight without feeling stuffed?
Use a small calorie surplus, not a daily food challenge. Gaining too fast mostly adds unnecessary fat and makes the process less comfortable. A modest surplus that you can sustain usually works better than force-feeding.
Add calories in forms that are easier to eat: oils, nut butters, avocado, whole eggs, full-fat dairy, rice, pasta, cereal, dried fruit, smoothies, and larger carbohydrate portions around training. In a gaining phase, lower-volume and more energy-dense foods are often useful because they create less fullness per calorie.
Keep protein sufficient, but not absurdly high. If protein is so high that it crowds out calories, reduce it to a reasonable level and use more carbohydrate and fat. Protein matters for muscle gain, but beyond a certain point it can become expensive, filling, and unnecessary.
Meal structure matters. Many people do better with three meals plus one or two snacks, or four to six smaller meals, rather than trying to cram all calories into a few large sittings. Eating again before you are ravenous can be easier than recovering from being overly full.
Liquid calories can help because they digest faster and create less fullness than large solid meals, but do not rely so heavily on shakes that digestion, energy, or appetite gets worse. Whole foods should still make up most of the diet.
If appetite is chronically poor, progress stalls for weeks, or eating enough feels miserable, reduce the target rate of gain and build calories gradually. The best gaining phase is one you can repeat consistently, not one that feels like punishment.