These can be smoothies, bars, drinks, supplements, etc.
Is there something specific you look for (ex. price, ingredients, specific nutrients etc.)?
Is there a brand you like / avoid (ex. soylent, huel, hol food, etc.)
Edit:
I definitely don't recommend fully replacing your diet with them. I know some people use them instead of other processed food / fast food / skipping meals entirely, and that's the use case I had in mind for myself
That's the thing, fad diets aren't bad by definition. As long as you're getting all your nutrients, it's fine, and you're unlikely to get malnutrition from replacing your breakfast with a shake, or a guava, or a steak.
If it helps you eat fewer calories, and doesn't overly hurt your micronutrients, it works.