Yes, depression comes in all shapes and sizes. If you imagine a line with depressed on one side and happy on the other, everyone on the planet will be somewhere on that line, meaning everyone experiences some form of depression sometimes. Depression is also not a static state, just like happiness or any other emotion. It changes week to week and day to day, although there may be period when it seems relatively static for a time.
There is episodic depression that might only remain for a few days, but will be incapacitating. There is depression that is mild but always in the background. There is depression that comes in waves. There are endless variations. Everyone who experiences depression experiences it uniquely. If you think of it like physical illness, some people might have an occasional cold but go about their day, or get the flu, and be out for a week once in a while, or get severe emphysema, and can only manage the basics.
So yes, there are people who are depressed who go about their life, without many people ever knowing they are depressed. They might do well academically, get a good job, get married, have kids, and appear to have an ideal life…..but inside they might be hurting most the time due to their depression.