I agree with the other coaches - don't be too fixated, be ready for anything (within and beyond FS). A couple of thoughts below…
- Practice casing, agnostic to industry: it is quite likely that interviews will focus on FSO cases, however EY will also want to test your general problem solving foundations - to do so, it's not uncommon to give an unexpected case from any industry - be ready for that.
- Build FS knowledge - given it's a specialist role, they will be expecting decent understanding of the industry - make sure you brush up on key macro trends & key topics, products, competitive landscape / players, growth segments, regulatory landscape & changes etc. Good way to do so is screening their corp website for reports and white papers + checking thought leadership articles from BCG perspectives, McKinsey Quarterly etc.
Finally, a connection from my network left the FSO practice quite recently - let me know if you'd like to get in touch for insider tips.
Hope this helps.