Fiber fills you up now by taking up physical volume. Try eating the equivalent of 200 calories of broc vs 200 calories of bread or pasta. The problem is that your body can't digest fiber so the digestive system moves it along quickly!

Fat and protein extends the feeling of satiation by turning off the hormonal signals for hunger.

If you eat an apple, try it with two tablespoons of peanut butter (the kind with only peanuts and salt). If you eat a serving of carrots, add two whole hard boiled eggs.

Carbs give a type of satiety I can't replicate with unlimited fat/protein/fibre. IMHO it's not actually hunger/stomach related but relief from withdrawal symptoms. Carbs are CNS stimulants that trigger serotonin release and very addictive to me at least.

After fasting or eating keto for a sufficient duration this carb specific form of absence/satiety no longer exists. Hunger/appetite stops feeling like a gnawing craving desire, instead it feels like a more neutral empty/weak signal.

Anyway, if eating carbs, best bang for buck satiety is the potato.