How to prepare for senior level software engineer interview?

Question

I am a full stack web developer with 9 years of experience. I am thinking of job change just because of my current company is still not done with their product for almost 7 years using the old techniques and technologies. I fear of becoming obsolete. I learnt React, Mongo, microservices on my own interest. I am very much interested in system design, wants to build highly scalable systems as an architect. What would be the expectation on senior software engineering position? Will they be asking more of data structures and algorithms or OOAD? How do I prepare for the new beginning? Thanks in advance.