Back in the day there was a converter application that let you move your Crusader Kings 2 games over to Europa Universalis 4. That was really neat, wasn't it? Would you like to do that with the newly-released and very excellent game Crusader Kings 3? Of course you would, and now thanks to modders (praised be their names) you can do just that. You can play nearly one thousand years of history, from Crusader Kings 3's 867 start to Europa Universalis 4's 1821 end.
I guess if you are also out of your mind you could then convert your game to Victoria 2 play that, and then convert to Hearts of Iron 4, because those converters exist. However, if you are not in charge of the whole world by 1948 I will be severely disappointed in you. You can find the converter mod on the Steam Workshop. It's still in development, but it works pretty well.
The CK3 to EU4 Converter is an application that takes your CK3 game and through various forms of dark magic converts it into a mod for EU4 that includes all your new, neat custom stuff in it. It's capable of converting games that are before EU4's start date of 1444, though you'll have to wait a bit to get the colonizing and technology-developing going. Otherwise, it preserves your cultures, religions, rulers, advisors, and more. It also has metrics for converting your many CK3 buildings into EU4 provincial development points.
You can read more about the nitty-gritty of how the converter works over on the Crusader Kings 3 wiki. It's made by the same team of folks who brought you the other Paradox grand strategy game converters—so if you know those you know what's up.
The modding scene for Crusader Kings 3 started at full tilt and kept going from there, with everything from vampires to bronze-age conquest offered and fantasy in the works. We've got a list of the best Crusader Kings 3 mods for you. We've also got an offering of weird and wonderful starting rulers to forge your thousand-year empire.
