Recommendation for preparing for multithreading/concurrency questions for System design round in tech interview?

What resources to use for the practice? What type of questions am I expected to use it - leetcode type, low level design type?

It is not hard to spin up multiple threads and create a practical parallel programming exercise so both of these are on the table. Parallel programming is something that's open to trivia as well like you can find here: https://interviewprep.org/parallel-processing-interview-questions/

I also recommend going through this: "How do I get better at building Large scale systems without working directly on such projects?"

You should ask the recruiter how practical this round will be (is it just a high-level knowledge test, local problem like LeetCode, or practical exercise like building out a live API that does parallel processing). From there, adjust accordingly.

I need a few examples to know what to expect for Rubrik interview? Or any company that says they would ask those questions in system design round.

Rubrik is a pretty big and well-known company. It's not exactly Big Tech, but it's approaching that scale. Check out the advice here to learn how to get examples: "How to figure out what's going to be on an interview?"

Are you in touch with the recruiter at Rubrik? The best source of information will be to ask them what to expect on the interview, or to ask people you know at Rubrik. See this question How to figure out what's going to be on an interview?

Phrasing is important: you're not asking for a list of questions/answers. Instead, you're asking for general guidelines on how they assess candidates and what the format will be.