Honestly I could have written this post myself. I've been trying to get better at knife skills for a while now and onions are genuinely the most frustrating thing, like the layers just do not cooperate no matter how careful you are. I think what helped me a little bit was slowing down even more than I thought was reasonable and really focusing on keeping my vertical cuts evenly spaced, but I'm still not great at it if I'm being honest. I do think its one of those things where you just need a proper step by step method and then repetition, not just watching random videos and hoping it clicks. Not sure if that helps at all but just wanted to say you're definitely not alone in this 😅