Well, I think at least in medieval-style fantasy stories, the evil sibling trope is something that comes out of the history of upper-class families in many societies, where brothers in particular were often at each others' throats for inheritance rights. That dynamic gets deliberately injected into foundational books of the genre and then trickles down into books influenced by those classics.
I think dynamics like that are really interesting if the siblings also love each other. Loving each other and being consciously in competition with one another is an interesting relationship to mine. In the novel I'm posting now, my MC had two cousins who are really his siblings in all but name, and they love each other but have relationships that grow increasingly strained because their goals are at odds.
But I'm also in the middle of writing a novel about a royal succession where the main character is an adviser to one of a set of brothers all vying for the throne. They are constantly scheming, plotting, and backstabbing, and it's fun as hell tbh.
Irl, I have two siblings I'm very close to, and I would never frame one for embezzlement in order to secure my own inheritance (only partially because the inheritance I would be backstabbing them over is primarily a storage building full of broken furniture my mom erroneously insists are priceless antiques).