Getting rejected after interviews even though I feel prepared. What am I missing?

I have been trying to switch jobs for the past few months. I have been preparing consistently: solving coding problems going through system design basics revising core concepts On paper I feel reasonably prepared. But in interviews, I’m not converting. One pattern I have noticed: When I explain my approach, I feel like my answers are not coming out clearly. I jump between ideas, miss assumptions, or can’t explain trade-offs properly. After the interview, I can see what I should have said, but in the moment it doesn’t come out right. So now I’m wondering if I’m missing something in my preparation. For people who were in a similar situation: What actually helped you start converting interviews?