I am in infosec (primarily, there's a lot of similar work I do that doesn't neatly bucket into that including finance). No leetcode required (except for security engineering roles, possibly). This obviously does not apply to SWEs, so plan accordingly. The interviews are the practice/prep for each subsequent interview. Think of it like Toastmasters [1] but for your career. Leetcode polishing does sound like it might work for SWEs, but I cannot speak to it, and don't want to provide bad advice (which can be worse than no advice).

[1] https://www.toastmasters.org/