Specific & Fast SEO Advice Needed

I am starting to get serious with SEO and I have having reasonable results, using SEMRush to develop onsite, offsite, technical aspects and it is starting to show in my visibility and ranking scores.

However, the largest search term in my (very niche) category is eluding me and despite very closely related terms starting to move into top 20/top10 etc, I am still not able to move even into the top 100 for this term.

I don't need generic SEO advice - SEMrush is giving me the analytics on that - I need somebody to have a look at the specific term and see what I am missing. So I imagine it's a quick job...but needs experience.

I am not planning to reveal the terms publicly, so please don't send messages asking for that as "clarification"