I think in my entire time working I haven't met anyone who has significantly contributed to open source (aside from "let me fix some bug that's annoying me in a library"), so I'm not sure how required it really is
It varies on focus area. Most big OSS projects are infrastructural in nature, and so if you're working in that space there's actually a lot of engineers who you meet with OSS experience beyond fixing random bugs. Even then, for every OSS engineer doing big OSS contributions, there are many who never do, it's just the nature of the business. I know of just one hiring decision (out of hundreds and hundreds) that was made because of OSS contributions, and I know no interviewers who routinely checked OSS contributions beyond surface level.