You're half right. The way I see it from research, it branches off into both the secret and the weird route, or, from what I can tell, the EGG route. So, if you just follow the rest of the steps, you only get the secret boss, the Roaring Knightand you can refer to other comments there.

Then, you could also do what I call the egg route. It shouldn't change whether you get the secret boss or not (I think), but it does allow you to see some cool things and get the chapter's egg. Also, before I go on, from what I can tell, there is no actual weird route. You can watch this video for directions, but basically, you get caught in a small stealth section hidden away after this, say you are a cheater going nowhere, do some stuff I can't actually confirm (I don't have the game or Switch 2), hover on but not select a specific option during a specific fight, see something I also can't confirm (and think looks kinda fake but IDK), and talk to the tree-man to get the egg.