How to avoid (almost) instant defeat when heirs take over

I got Crusader Kings III some time ago, as part of Game Pass. Played it quite a lot, but all my games ended more or less the same way: Once my initial character dies and an heir takes over, all hell breaks lose. Factions creating against me left and right, people hate my heir and declares war over nothing (that's what it feels like anyway).

Eventually I kind of gave up on the game. Fast forward about half a year and here I am, wanting to give the game a second chance... And the same thing happens.

I feel like I am missing something super obvious. This time I even turned down the difficulty to "Very easy". With my initial character I expanded my kingdom quite noticeably. There was bumps on the road of course, but generally I felaat it went well and I was in control and won the wars I got in. Then my character dies and his heir takes over. This time it took about five years before I got dragged into war and then it felt like a domino effect from there. As said, factions rising all over my kingdom and my neighbours going to war against me for more or less good reasons.

I know it all sounds kind of vague and whiny. I apologize for that. I really find this game fun and interesting, but it's also incredibly frustrating to see all your hard work be lost when you need to hand over the kingdom to an heir.

As said, it feels like I'm missing some obvious key aspect of the game. I may not be a great strategist, but I feel that on "Very easy" I should be able to more or less leisurely cruise through the game? If anyone has good pointers, tips or tricks, I will gladly hear about it. I started a new game once more, this time reducing factions to a minimum. I hope that will help me once my first ruler dies.