The operation is as follows:
After the input method is adjusted, press ~ to open the cheats.
Then enter allow_laws.
Raise the kingship to middle kingship and above, but suggest middle kingship.
The promotion of kingship requires a vassal vote, and if it fails, it will send money to those who oppose it.
After passing the kingship, you can choose the eldest son inheritance law.
After the adjustment of your law of succession to titles and kingship,
If the next title is usurped, the law of succession and kingship will be very chaotic.
It can directly destroy the reconstruction, just like your main title.
Perfect.