Yeah, like others are saying, this is not a game with a typical "victory." It has an "ending," of course, when the timeline ends, or when your dynasty dies, but the game itself has no pre-set goal. The goal is whatever you decide it to be. Essentially it is a simulator, and you are "winning" if you are having fun playing it.
This is what I've found out. Sense the show vikings is my inspiration, I'm playing as Alfred. So far I have Mercia, Angela and Wessex. Currently I'm trying to decide to either go for Gweynny to bolster my forces, or attack Jorvik.
There is no "victory" in CK3 per se. It's (almost) a pure sandbox. The game continues until your line ends or you reach 1453.
You make your own victory conditions. Painting the map in a world conquest is an obvious one, but lots of folks like to do roleplay runs for particular historical figures, thematic runs (e.g super intrigue focus, building "tall" to keep a small realm independent through the whole run), etc.
There are lots of significant achievements that are almost a mini-victory, restoring Rome for example, but there's no "winning." There is definitely losing, though.