I haven't done any Leetcode so I have no idea of what "medium"/"hard"/etc are, but the last time I interviewed, the two problems I failed were very fiddly dynamic programming problems—the hard part was not even the dynamic programming, but rather the problem-specific setup (based on chess rules and geometry, respectively).

I am sure I would have done better at those with practice, entirely because I would have seen lots more fiddly dynamic programming problems and not because I would have picked up any general-purpose skills or knowledge I don't have as-is.