The patch notes say something like, you can see vassals by ctrl-clicking. On what, though? Noob question I know... It sounds useful!
Ctrl+click on the map (not the minimap, the big map that you do everything on), and it'll show direct vassals. You can do it again to show the vassals of a vassal. Ctrl+right-click to go in the other direction (e.g. if you ctrl+clicked twice, you'll need to ctrl+right-click twice to go back to seeing the full realm).
Also note that in CK3 (contrary to CK2), you automatically see vassals of a realm if you are yourself a vassal of that realm, and can only see the realm as a whole if you either have the ruler selected, or zoom out to the paper map. Ctrl+right-click does not work here.
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