You want to hit your macros which depends on your BMI I do a different style and do carnivore some people do keto because it helps speed up the process of fat loss, so you can but should hit those important macros. Also whatever you want in the context of a lot of food, I would say no to that but the benefit of OMAD is by the time you eat you really aren’t all that hungry anyway
Physics still apply , calories in and out and all that stuff
Fasting and OMAD will help you cut down on snacking calories, build better habits, so in a way, yes you can eat whatever you want, if it ends up being less caloric than what you ate before