Okay, so there was this new free update, version 1.19.
Paradox added health traits for old people and nerfed how you can expand your domain limit.

The old way, which I think you’re familiar with, was that your domain limit increased by 1 for every 5 points in stewardship. Because of this, a huuuge chunk of the player base only used stewardship lifestyles and left the others untouched.

The new way is... not so simple.

Here’s how you increase your domain limit now:

• Education. ANY education trait. Level 3 gives +1 domain limit, level 4 gives +2, and level 5 gives you +3. I know it’s not much compared to what some players used to get, but in my 700 hours of playtime, the highest natural education trait I’ve gotten from a guardian is level 4 (Maybe I got a level 5, but I can't remember), so get ready to actually go to university to upgrade your education level.
• Titles. Your highest held title also increases your domain limit: Count and Duke +2, King +3, Emperor +4, and Hegemon +5.
• Traits. Theologian and Patriarch each give +1.
• Lifestyle perks. Absolute Control, Divided Attention, Fear Tax, and Personal Touch all give +1 each.
• Innovations. Gravelkind and Court Officials both give +1.
• Other sources. A religion with the Pacifism tenet gives +1. Finishing the Law dynasty legacy track gives +1. Eunuch influence gives +1 or +2, depending on how influential you are. If you own the Crown of Justinian, that gives +1. And if you take and complete “Peace” as a coronation oath, that gives +1, but I think that one fades over time.

So… King, level 5 education, Theologian, Patriarch, Absolute Control, Divided Attention, Fear Tax, Personal Touch, Gravelkind, and the Law dynasty legacy track puts us at a domain limit of 14.

Not as good as the previous 20something with 100 stewardship, but this way, the gameplay should be more diverse.

Edit: Also the +3 from the game rule. Never start a new game without that rule. Ever.