A big part of being a ruler in Crusader Kings is being at the centre of plots, whether you want to steal a title from someone or just murder a particularly smug vassal. In Crusader Kings 3, all that plotting and scheming returns, along with some new systems that let you influence people even more.
Crusader Kings 2's plots have been replaced with the Scheme system, but judging by the new dev diary, it should still be fairly familiar. If you want to assassinate someone, you find some co-conspirators, wait around for a bit, and then maybe they'll be killed, but the job might also be botched.
Instead of being able to try and recruit everyone in the realm, you only need a few fellow plotters, so you should try to find people close to your target. Then, every month, your assassination scheme will have a chance to progress, based on the skills and modifiers of both schemer and victim, and who you've recruited to the cause. Once it hits the tenth step, the assassination will take place, though not always successfully. Until you try to execute your scheme, you won't be discovered, but your helpers won't have the same protection. If you join a plot, you'll similarly be at risk.
The Scheme system isn't just for plotting murders—there's romance, too. Seduction returns, but it's been bundled into the new system. You won't need to recruit anyone, and success will depend on seduction skill, sexual preference and if they actually like you. Like CK2, seduction is good way to get people to join your other schemes. And if you don't want to get romantic but still want to influence people, you can once again sway them with diplomacy.
The broad strokes are the same, but it's also accompanied by two new systems, Secrets and Hooks. Secrets are collected as you do naughty or taboo things, like murder or becoming a monarch's bit on the side, and if they're discovered they can be used against you. Thankfully, you can do the same to other characters, sending out your spy to look through their dirty laundry. Secrets can then be exposed, or they could be used as leverage, using them to blackmail someone into joining a scheme. And if you can't find any dirt, you can always try to make something up.
It's good to see Crusader Kings 3 will let us continue to be our very worst selves.